Clean up accessibility gestures.

Closing two small holes in the implementation:
1. The gesture was dispatched before the callback was registered. It
was possible for gestures that failed quickly to fail to report any
status.
2. Gestures could be dispatched before the input filter was
installed. Adding a wait to give the filter a chance to install
before reporting a failure.

Also removing an unused method on the input filter.

Change-Id: I77cd80dcd2cec6c72b3761169aba5eaecf62250b
(cherry picked from commit 03465fb8)