compositor: remove android backend

compositor: remove android backend

The Android backend has been fairly unused, since we do not have
projects actively using it. It gets basic build testing as part of the
normal build, but runtime testing it takes a considerable effort, and so
I have not done that in a long time. The code is slowly rotting, and
with new emerging backends it starts to be a burden, since it cannot use
udev, but needs evdev.

Therefore to ease Weston going forward, remove the Android backend. If
someone misses it, it can still be found in the stable 1.0 branch, and
of course resurrected from git history if someone wants to put in the
effort and maintain it.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>