Remove synamic modern event system flag for FB (#19059)

* Remove synamic modern event system flag for FB

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

@@ -17,7 +17,6 @@ export const warnAboutSpreadingKeyToJSX = __VARIANT__;
 export const enableComponentStackLocations = __VARIANT__;
 export const disableInputAttributeSyncing = __VARIANT__;
 export const enableFilterEmptyStringAttributesDOM = __VARIANT__;
-export const enableModernEventSystem = __VARIANT__;
 export const enableLegacyFBSupport = __VARIANT__;
 export const enableDebugTracing = !__VARIANT__;
 

packages/shared/forks/ReactFeatureFlags.www.js

@@ -21,7 +21,6 @@ export const {
   disableSchedulerTimeoutBasedOnReactExpirationTime,
   warnAboutSpreadingKeyToJSX,
   replayFailedUnitOfWorkWithInvokeGuardedCallback,
-  enableModernEventSystem,
   enableFilterEmptyStringAttributesDOM,
   enableLegacyFBSupport,
   enableDebugTracing,
@@ -73,6 +72,8 @@ export const disableTextareaChildren = __EXPERIMENTAL__;
 
 export const warnUnstableRenderSubtreeIntoContainer = false;
 
+export const enableModernEventSystem = true;
+
 // Enable forked reconciler. Piggy-backing on the "variant" global so that we
 // don't have to add another test dimension. The build system will compile this
 // to the correct value.

scripts/rollup/modules.js

@@ -16,6 +16,7 @@ const importSideEffects = Object.freeze({
   'react-dom/server': HAS_NO_SIDE_EFFECTS_ON_IMPORT,
   'react/jsx-dev-runtime': HAS_NO_SIDE_EFFECTS_ON_IMPORT,
   'react-fetch/node': HAS_NO_SIDE_EFFECTS_ON_IMPORT,
+  'react-dom': HAS_NO_SIDE_EFFECTS_ON_IMPORT,
 });
 
 // Bundles exporting globals that other modules rely on.