Replaced current owner forward with current:null

Author: Brian Vaughn

packages/shared/ReactSharedInternals.js

@@ -10,18 +10,13 @@ import React from 'react';
 const ReactSharedInternals =
   React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED;
 
-// Add fallback for newer renderers running with older react package versions.
+// Prevent newer renderers from RTE when used with older react package versions.
 // Current owner and dispatcher used to share the same ref,
 // but PR #14548 split them out to better support the react-debug-tools package.
 if (!ReactSharedInternals.hasOwnProperty('ReactCurrentDispatcher')) {
   const {ReactCurrentOwner} = ReactSharedInternals;
   ReactSharedInternals.ReactCurrentDispatcher = {
-    get current() {
-      return ReactCurrentOwner.currentDispatcher;
-    },
-    set current(value) {
-      ReactCurrentOwner.currentDispatcher = value;
-    },
+    current: null,
   };
 }