Repository: facebook/react
Pull request: opt: optimize the judgement of supportsHydration

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## Summary

The variable `supportsHydration` has been judged on [line 1354](https://github.com/zh-lx/react/blob/main/packages/react-reconciler/src/ReactFiberBeginWork.new.js#L1354), when the code executes to [line 1402](https://github.com/zh-lx/react/blob/main/packages/react-reconciler/src/ReactFiberBeginWork.new.js#L1402), the value of `supportsHydration` must be `true`. So it doesn't need to be judged again.

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## How did you test this change?

It does not need to add additional tests.
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Changed files:
filename: packages/react-reconciler/src/ReactFiberBeginWork.new.js
patch: @@ -1399,7 +1399,7 @@ function updateHostRoot(current, workInProgress, renderLanes) {
     } else {
       // The outermost shell has not hydrated yet. Start hydrating.
       enterHydrationState(workInProgress);
-      if (enableUseMutableSource && supportsHydration) {
+      if (enableUseMutableSource) {
         const mutableSourceEagerHydrationData =
           root.mutableSourceEagerHydrationData;
         if (mutableSourceEagerHydrationData != null) {

filename: packages/react-reconciler/src/ReactFiberBeginWork.old.js
patch: @@ -1399,7 +1399,7 @@ function updateHostRoot(current, workInProgress, renderLanes) {
     } else {
       // The outermost shell has not hydrated yet. Start hydrating.
       enterHydrationState(workInProgress);
-      if (enableUseMutableSource && supportsHydration) {
+      if (enableUseMutableSource) {
         const mutableSourceEagerHydrationData =
           root.mutableSourceEagerHydrationData;
         if (mutableSourceEagerHydrationData != null) {