dillon1000/react

Fix double-firing submit events (#12877)

We were adding a listener at the root when we weren't meant to. Blames to e96dc140599363029bd05565d58bcd4a432db370.

This now alerts once (at FORM) instead of twice (at FORM, #document):

```
var Hello = class extends React.Component {
  render() {
    return (
      <form onSubmit={(e) => {e.preventDefault(); alert('hi ' + e.nativeEvent.currentTarget.nodeName);}}>
        <button>hi</button>
      </form>
    );
  }
};
```