Remove duped flushSync warning from linked React docs

Author: brophdawg11

docs/hooks/use-fetcher.md

@@ -137,8 +137,6 @@ If you find yourself calling this function inside of click handlers, you can pro
 
 The `unstable_flushSync` option tells React Router DOM to wrap the initial state update for this `fetcher.load` in a [`ReactDOM.flushSync`][flush-sync] call instead of the default [`React.startTransition`][start-transition]. This allows you to perform synchronous DOM actions immediately after the update is flushed to the DOM.
 
-<docs-warning>`ReactDOM.flushSync` de-optimizes React and can hurt the performance of your app.</docs-warning>
-
 <docs-warning>Please note that this API is marked unstable and may be subject to breaking changes without a major release</docs-warning>
 
 ### `fetcher.submit()`

docs/hooks/use-navigate.md

@@ -93,8 +93,6 @@ The `unstable_flushSync` option tells React Router DOM to wrap the initial state
 
 <docs-warning>`unstable_flushSync` only works when using a data router, see [Picking a Router][picking-a-router]</docs-warning>
 
-<docs-warning>`ReactDOM.flushSync` de-optimizes React and can hurt the performance of your app.</docs-warning>
-
 <docs-warning>Please note that this API is marked unstable and may be subject to breaking changes without a major release</docs-warning>
 
 ## `options.unstable_viewTransition`

docs/hooks/use-submit.md

@@ -164,8 +164,6 @@ Because submissions are navigations, the options may also contain the other navi
 
 The `unstable_flushSync` option tells React Router DOM to wrap the initial state update for this submission in a [`ReactDOM.flushSync`][flush-sync] call instead of the default [`React.startTransition`][start-transition]. This allows you to perform synchronous DOM actions immediately after the update is flushed to the DOM.
 
-<docs-warning>`ReactDOM.flushSync` de-optimizes React and can hurt the performance of your app.</docs-warning>
-
 <docs-warning>Please note that this API is marked unstable and may be subject to breaking changes without a major release</docs-warning>
 
 [pickingarouter]: ../routers/picking-a-router