Revert "Set disableLegacyMode to true for www (#29871)"

This reverts commit fb9a90f.

Author: kassens

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

@@ -32,6 +32,7 @@ export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
 export const enableAddPropertiesFastPath = __VARIANT__;
+export const disableLegacyMode = __VARIANT__;
 
 // Enable this flag to help with concurrent mode debugging.
 // It logs information to the console about React scheduling, rendering, and commit phases.

packages/shared/forks/ReactFeatureFlags.www.js

@@ -119,7 +119,8 @@ export const useModernStrictMode = true;
 // because JSX is an extremely hot path.
 export const disableStringRefs = false;
 
-export const disableLegacyMode = true;
+export const disableLegacyMode: boolean =
+  __EXPERIMENTAL__ || dynamicFeatureFlags.disableLegacyMode;
 
 export const enableOwnerStacks = false;
 export const enableShallowPropDiffing = false;