Do not use surface crop as touchable region in standard task

This fixes a refactoring error introduced by commit 3213c965.
This change restores the original logic that if a window is in a
task which should crop touchable region by root task, then just
set the root task surface but not replace the region directly.
Otherwise the touchable region of a sub window may occupy the
entire screen.

Bug: 172522375
Test: WindowStateTests#testUpdateInputWindowHandle
      LoginActivityTest#testAutofillTapOutside
Change-Id: I771b44515c6f70ae3713d3b69658497782dde92c