[64/n] Remove dependency on DesksOrganizer

Remove the dependency between SkipLetterboxLifecycleEventFactory
and DesksOrganizer. This also allows other form factors to use
Letterbox without unrelated dependencies (e.g. Desktop Windowing).

Flag: EXEMPT Refactoring
Bug: 423915680
Test: atest WMShellUnitTests:SkipLetterboxLifecycleEventFactoryTest

Change-Id: I7a0a5797754e7b550dd61d7316d16e7e99a972e7