When ANR happens, only remove ANR'd window.

The system bar uses input event injection to inject BACK keys
into the application.  If the receiving application ANRs, we
used to clear the touch state unconditionally.  Doing so would
prevent the system bar from receiving the ACTION_UP event so
the back button would continue to appear pressed until pressed
again.

Now we are more careful to only remove the specific ANR'd
window from the touch state.  Other windows should continue
to receive touch events as usual.

Change-Id: If86bfc323e2c7aed82ca1334bc67da649953168f