Remove redundant logic about System UI visibility

This CL removes
- mSeq
- System UI flags used to communicate between WMS and System UI
- redundant AIDL methods
- redundant fields and methods
- redundant tests
- PolicyControl

This CL also
- refines the format in DisplayPolicy#dump
- sends a boolean to InputManager to indicate if System UI is in a low
  profile mode instead of sending the legacy system UI visibility

Bug: 149813814
Fix: 169105126
Test: presubmit
Test: dumpsys window displays
Test: See if the layout of ImmersiveModeConfirmation is as expected
Change-Id: I8c8df509355bebc9b560af57d5458614557bcd2f