docs: Fixing controller support example for bug 22727418 and 24098562

As per Robert Anderberg's recommendation, removed the manifest example that
doesn't include android:required="false" and updated description text to
indicate the example works with apps that "support" a game controller rather
than "require". Updated Robert's suggestion with more concise version from
Andrew's suggestion. Note that we're not adding info on specifying
android:required="true" because this causes the app to not be installable on
any devices (because controllers aren't currently considered part of a device,
so it ends up looking like no devices have controllers at install time)

Bug: 22727418
Bug: 24098562
Change-Id: Ie4dd02d5599b9ffda53e46dc5af4765d888e81a4