Land useModernStrictMode in www (facebook#28696)

this has landed

Author: rickhanlonii

packages/shared/forks/ReactFeatureFlags.www-dynamic.js

@@ -28,7 +28,6 @@ export const alwaysThrottleRetries = __VARIANT__;
 export const enableDO_NOT_USE_disableStrictPassiveEffect = __VARIANT__;
 export const enableUseDeferredValueInitialArg = __VARIANT__;
 export const enableRenderableContext = __VARIANT__;
-export const useModernStrictMode = __VARIANT__;
 export const enableRefAsProp = __VARIANT__;
 export const enableRetryLaneExpiration = __VARIANT__;
 export const favorSafetyOverHydrationPerf = __VARIANT__;

packages/shared/forks/ReactFeatureFlags.www.js

@@ -36,7 +36,6 @@ export const {
   transitionLaneExpirationMs,
   enableInfiniteRenderLoopDetection,
   enableRenderableContext,
-  useModernStrictMode,
   enableRefAsProp,
   favorSafetyOverHydrationPerf,
 } = dynamicFeatureFlags;
@@ -109,6 +108,7 @@ export const enableServerComponentKeys = true;
 export const enableServerComponentLogs = true;
 
 export const enableReactTestRendererWarning = false;
+export const useModernStrictMode = true;
 
 // TODO: Roll out with GK. Don't keep as dynamic flag for too long, though,
 // because JSX is an extremely hot path.