Updates internal lock task mode state early

When removing a lock task, LockTaskController callbacks status bar on
the lock task mode state change. On the receiver side, SysUI queries
ActivityTaskManager#getLockTaskModeState to updates its SysUiState.

This raises a race condition that SysUI gets a staled lock task state
and uses that info to disable Recents.

PinnedStackTests#testPinnedStackWithDockedStack is flaky since it's
running after PinnedStackTests#testDisallowEnterPipActivityLocked and
relies on Recents being functional.

Bug: 156003518
Test: atest --iteration 5 PinnedStackTests
Change-Id: I1ff3c75c4ad37ee8f3951b8f2d7f2a3b0f8334ce