Clean up enableSyncDefaultUpdates flag a bit (#26858)

## Overview

Does a few things:
- Renames `enableSyncDefaultUpdates` to
`forceConcurrentByDefaultForTesting`
- Changes the way it's used so it's dead-code eliminated separate from
`allowConcurrentByDefault`
- Deletes a bunch of the gated code

The gates that are deleted are unnecessary now. We were keeping them
when we originally thought we would come back to being concurrent by
default. But we've shifted and now sync-by default is the desired
behavior long term, so there's no need to keep all these forked tests
around.

I'll follow up to delete more of the forked behavior if possible.
Ideally we wouldn't need this flag even if we're still using
`allowConcurrentByDefault`.

DiffTrain build for commit 018c58c.

Author: rickhanlonii

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-dev.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<ca59e5754dbc2396cdc2b7d218cedd13>>
+ * @generated SignedSource<<e2649a21f4471fab672f885dc7d27434>>
  */
 
 'use strict';
@@ -23529,8 +23529,6 @@ function createHostRootFiber(
     }
 
     if (
-      // We only use this flag for our repo tests to check both behaviors.
-      // TODO: Flip this flag and rename it something like "forceConcurrentByDefaultForTesting"
       // Only for internal experiments.
       concurrentUpdatesByDefaultOverride
     ) {
@@ -23930,7 +23928,7 @@ function createFiberRoot(
   return root;
 }
 
-var ReactVersion = "18.3.0-canary-ae31d2ea3-20230531";
+var ReactVersion = "18.3.0-canary-018c58c9c-20230601";
 
 // Might add PROFILE later.
 

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-prod.js

@@ -8617,7 +8617,7 @@ var devToolsConfig$jscomp$inline_1036 = {
     throw Error("TestRenderer does not support findFiberByHostInstance()");
   },
   bundleType: 0,
-  version: "18.3.0-canary-ae31d2ea3-20230531",
+  version: "18.3.0-canary-018c58c9c-20230601",
   rendererPackageName: "react-test-renderer"
 };
 var internals$jscomp$inline_1235 = {
@@ -8648,7 +8648,7 @@ var internals$jscomp$inline_1235 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-canary-ae31d2ea3-20230531"
+  reconcilerVersion: "18.3.0-canary-018c58c9c-20230601"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_1236 = __REACT_DEVTOOLS_GLOBAL_HOOK__;

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react-test-renderer/cjs/ReactTestRenderer-profiling.js

@@ -9043,7 +9043,7 @@ var devToolsConfig$jscomp$inline_1078 = {
     throw Error("TestRenderer does not support findFiberByHostInstance()");
   },
   bundleType: 0,
-  version: "18.3.0-canary-ae31d2ea3-20230531",
+  version: "18.3.0-canary-018c58c9c-20230601",
   rendererPackageName: "react-test-renderer"
 };
 var internals$jscomp$inline_1276 = {
@@ -9074,7 +9074,7 @@ var internals$jscomp$inline_1276 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-canary-ae31d2ea3-20230531"
+  reconcilerVersion: "18.3.0-canary-018c58c9c-20230601"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_1277 = __REACT_DEVTOOLS_GLOBAL_HOOK__;

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-dev.js

@@ -27,7 +27,7 @@ if (
 }
           "use strict";
 
-var ReactVersion = "18.3.0-canary-ae31d2ea3-20230531";
+var ReactVersion = "18.3.0-canary-018c58c9c-20230601";
 
 // ATTENTION
 // When adding new symbols to this file,

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-prod.js

@@ -642,4 +642,4 @@ exports.useSyncExternalStore = function (
   );
 };
 exports.useTransition = useTransition;
-exports.version = "18.3.0-canary-ae31d2ea3-20230531";
+exports.version = "18.3.0-canary-018c58c9c-20230601";

compiled-rn/facebook-fbsource/xplat/js/RKJSModules/vendor/react/cjs/React-profiling.js

@@ -645,7 +645,7 @@ exports.useSyncExternalStore = function (
   );
 };
 exports.useTransition = useTransition;
-exports.version = "18.3.0-canary-ae31d2ea3-20230531";
+exports.version = "18.3.0-canary-018c58c9c-20230601";
 
           /* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */
 if (

compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/REVISION

@@ -1 +1 @@
-ae31d2ea3c3f9f0a87ff2c6193484d5d8786bc5f
+018c58c9c65452cff25aaf1f38f78a9b90d8e5c1

compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/implementations/ReactFabric-dev.fb.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<130672a53893af8813c0dcaa40c799e0>>
+ * @generated SignedSource<<4a2e654ac2f9287b5e09859cfc8873f1>>
  */
 
 'use strict';
@@ -26786,8 +26786,6 @@ function createHostRootFiber(
     }
 
     if (
-      // We only use this flag for our repo tests to check both behaviors.
-      // TODO: Flip this flag and rename it something like "forceConcurrentByDefaultForTesting"
       // Only for internal experiments.
       concurrentUpdatesByDefaultOverride
     ) {
@@ -27246,7 +27244,7 @@ function createFiberRoot(
   return root;
 }
 
-var ReactVersion = "18.3.0-canary-4ecba8f8";
+var ReactVersion = "18.3.0-canary-14cb1992";
 
 function createPortal$1(
   children,

compiled-rn/facebook-fbsource/xplat/js/react-native-github/Libraries/Renderer/implementations/ReactNativeRenderer-dev.fb.js

@@ -7,7 +7,7 @@
  * @noflow
  * @nolint
  * @preventMunge
- * @generated SignedSource<<6bfa1b804011279825ec23eadae41f68>>
+ * @generated SignedSource<<c72d55f3b541b5fe0820ed08c05813c8>>
  */
 
 'use strict';
@@ -27300,8 +27300,6 @@ function createHostRootFiber(
     }
 
     if (
-      // We only use this flag for our repo tests to check both behaviors.
-      // TODO: Flip this flag and rename it something like "forceConcurrentByDefaultForTesting"
       // Only for internal experiments.
       concurrentUpdatesByDefaultOverride
     ) {
@@ -27760,7 +27758,7 @@ function createFiberRoot(
   return root;
 }
 
-var ReactVersion = "18.3.0-canary-2ce08e7a";
+var ReactVersion = "18.3.0-canary-e9eddf24";
 
 function createPortal$1(
   children,