Make WindowContainer stop implementing InsetsControlTarget

This should be done in commit e1b363d5
or it shouldn't be done in commit
f60944f1 in the first place. Because
non-WindowState WindowContainer never becomes a control target of any
source.

Bug: 199449177
Bug: 281029564
Flag: EXEMPT clean up
Test: presubmit
Change-Id: I594b5d286d47f6d0de298d9947de5de7f505d8d7