Remove less useful tests
This MR removes a number of less useful tests. The end users will very likely use libinput for all input, so it does not make sense to spend time fixing input driver tests, especially since they are no longer fully reproducible due to race conditions introduced by the implementation of the input thread.
Additionally, a test for the DGA extension has been removed. It has been deprecated in the release notes for at least since 2012, so it no longer makes sense to spend time on it.
@whot: Do you think it would make sense to just go ahead and remove DGA from xserver master?