Remove getIsHydrating (#18019)

packages/react-dom/src/client/ReactDOMFB.js

@@ -7,7 +7,6 @@
  * @flow
  */
 
-import {getIsHydrating} from 'react-reconciler/src/ReactFiberHydrationContext';
 import {addUserTimingListener} from 'shared/ReactFeatureFlags';
 
 import ReactDOM from './ReactDOM';
@@ -26,8 +25,6 @@ Object.assign(
     },
     // Perf experiment
     addUserTimingListener,
-
-    getIsHydrating,
   },
 );
 

packages/react-reconciler/src/ReactFiberHydrationContext.js

@@ -484,10 +484,6 @@ function resetHydrationState(): void {
   isHydrating = false;
 }
 
-function getIsHydrating(): boolean {
-  return isHydrating;
-}
-
 export {
   warnIfHydrating,
   enterHydrationState,
@@ -498,5 +494,4 @@ export {
   prepareToHydrateHostTextInstance,
   prepareToHydrateHostSuspenseInstance,
   popHydrationState,
-  getIsHydrating,
 };