deps: Upgrade to RN v0.66.4!

Note: If you get an error like

  CocoaPods could not find compatible versions for pod "RCT-Folly"

on `yarn` or `pod install` when crossing this commit (checking out a
branch that has it from one that doesn't, or vice versa), run
`pod update RCT-Folly` from `ios/` and try the command again.
Background:
  facebook/react-native#32659 (comment)

In this commit:

- Bump `react-native` and `flow-bin` versions

- Suppress a few errors from the new Flow version (see comments)

- Remove react-native-codegen, following the template-app change in
  facebook/react-native@ab829005b

- Add a hack line to the Podfile, following the template-app change
  in facebook/react-native@ea5109fc0

.flowconfig

@@ -123,4 +123,4 @@ module.file_ext=.ios.js
 exact_by_default=true
 
 [version]
-^0.149.0
+^0.158.0

ios/Podfile

@@ -23,6 +23,7 @@ target 'ZulipMobile' do
 
   post_install do |installer|
     react_native_post_install(installer)
+    __apply_Xcode_12_5_M1_post_install_workaround(installer)
   end
 
   use_expo_modules!