Compare binder instead of the proxy for DisplayAreaOrganizer

Before, we directly compared the da.mOrganizer when unregister, which
failed to remove it. Now, we compare the binder instead.

Bug: 169224778
Test: manual: test with OneHanded mode
Test: atest WmTests:DisplayAreaOrganizerTest
Change-Id: I907615c111b10787dfb53b6fe2f683d651c21b23