Update docs for Text allowFontScaling

Summary:
> Explain the **motivation** for making this change. What existing problem does the pull request solve?

The documentation was slightly out of date. Following facebook#10898, which removed the `platform ios` tag, this updates the inner documentation to remove the reference to iOS.
Closes facebook#11993

Differential Revision: D4443723

Pulled By: hramos

fbshipit-source-id: b859c9b0fe1f5e564b919663f8c75401a52ffc9f

Libraries/Text/Text.js

@@ -176,7 +176,7 @@ const Text = React.createClass({
      */
     testID: PropTypes.string,
     /**
-     * Specifies whether fonts should scale to respect Text Size accessibility setting on iOS. The
+     * Specifies whether fonts should scale to respect Text Size accessibility settings. The
      * default is `true`.
      */
     allowFontScaling: PropTypes.bool,