Ensure screenshot input monitor is always removed

We currently remove and dispose of the input monitor in View.onDetach.
However, it's possible for the screenshot process to get frozen
before that call actually occurs, which causes an ANR when the
screenshot process doesn't actually respond to input events. This
change adds a synchronous call to removeWindow to ensure that
the input monitor is never left around once the window is
removed.

Bug: 199592789
Test: manual -- forced a delay in detaching the view and stopping
the input listener, verified that the expected crash occurred,
and checked that adding the synchronous call fixes the problem

Change-Id: I0aff68ce4876082a5e20e3fe5f83cffcda4f6390