Remove Taskbar WindowToken upon onDisplayRemoved

This CLs removes DeviceProfile of the display before destroying the
taskbar in onDisplayRemoved(). This makes sure DeviceProfile is null
when destroyTaskbarForDisplay() is called in onDisplayRemoved(), so that
removeTaskbarRootViewFromWindow() can be executed when display mirroring
starts.

Bug: 401180264
Test: adb shell settings put secure mirror_built_in_display 1
Flag: EXEMPT bug fix
Change-Id: I42cb8a1ecfdf1aa57d8ee3d01242a156f8a92cd9