1/n remove GK on flushSync

Summary:
This has been running in production for some time and causes no problems, in
sync or async. Let's remove the GK check and make it the default behavior where
supported.

Reviewed By: sophiebits

Differential Revision: D7116729

fbshipit-source-id: f590508ea50de9639d821e1f2c8556e20c8ac54f

src/component/base/DraftEditor.react.js

@@ -258,7 +258,7 @@ class DraftEditor extends React.Component<DraftEditorProps, State> {
       if (!this.props.readOnly) {
         const method = this._handler && this._handler[eventName];
         if (method) {
-          if (flushControlled && gkx('draft_js_flush_sync')) {
+          if (flushControlled) {
             flushControlled(() => method(this, e));
           } else {
             method(this, e);