Remove immersive task from repository when task is removed

When a task is removed from the active task list (i.e. it is no longer a
desktop task), make sure to mark it as no longer immersive if it was
immersive.

This change also updates the persistence repository with a desktop id
(using display id as there are no desktops yet) because otherwise
multi-display unit tests always modify the same desktop, which is
causing failures if a second display's repository data is non-null.

Flag: com.android.window.flags.enable_fully_immersive_in_desktop
Fix: 378172979
Test: enter desktop immersive, exit desktop to fullscreen or split, go
back to desktop, verify immersive button is responsive and the task can
re-enter immersive.

Change-Id: I2dcf6a7acca34dc60ae15b2a725a0d05048468eb