Remove false annotation

Summary:
I'd love to add annotations letting people know that this function and a few others take `SyntheticEvent`s but that may be inconsistent with the rest of the docs. For now, this particular annotation should be removed
Closes https://github.com/facebook/react-native/pull/592
Github Author: Will Piers <wpiers@rallydev.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

Libraries/Components/TextInput/TextInput.js

@@ -217,8 +217,6 @@ var TextInput = React.createClass({
      */
     onFocus: PropTypes.func,
     /**
-     * (text: string) => void
-     *
      * Callback that is called when the text input's text changes.
      */
     onChange: PropTypes.func,