Remove server://singlefetch origin stub

packages/react-router/lib/dom/ssr/single-fetch.tsx

@@ -286,14 +286,7 @@ export function addRevalidationParam(
 export function singleFetchUrl(reqUrl: URL | string) {
   let url =
     typeof reqUrl === "string"
-      ? new URL(
-          reqUrl,
-          typeof window === "undefined"
-            ? // TODO: Trace usage of singleFetchUrl and make sure we don't use it anywhere
-              // this will make it to a network call.
-              "server://singlefetch/"
-            : window.location.origin
-        )
+      ? new URL(reqUrl, window.location.origin)
       : reqUrl;
   url.pathname = `${url.pathname === "/" ? "_root" : url.pathname}.data`;
   return url;