Refactor TestSplitOrganizer and remove useless code

Refactor TestSplitOrganizer to WINDOWING_MODE_MULTI_WINDOW and fix
related tests. And remove some tests and code if such behavior
should not apply to new split.

Bug: 199236198
Test: atest WmTests
Change-Id: I6461b1616f78e0396705c534e90b28374f3d9177