YellowBox: Restore ES5 Compatibility

Reviewed By: sahrens

Differential Revision: D8421561

fbshipit-source-id: c2b8d430f4d0c9ce0d5177f0af5eb5f404916024

Libraries/YellowBox/YellowBox.js

@@ -130,12 +130,11 @@ if (__DEV__) {
     }
   };
 
-  function registerWarning(...args): void {
+  const registerWarning = (...args): void => {
     YellowBoxRegistry.add({args, framesToPop: 2});
-  }
+  };
 } else {
-  // eslint-disable-next-line no-shadow
+  YellowBox = class extends React.Component<Props> {
-  YellowBox = class YellowBox extends React.Component<Props> {
     static ignoreWarnings(patterns: $ReadOnlyArray<string>): void {
       // Do nothing.
     }