Remove redundant instances of depth controller.

During each app launch, a new `MyDepthController` is instantiated, which
registers two of its methods as listeners for cross window blur and
opaqueness. This controller's usefulness spans that specific animation
only, but the listeners are never unregistered. This creates conflicts
when an opaqueness signal happens, which cause the background to flicker
(see videos).

Bug: 283335820
Test: manual, see videos in the bug
Flag: not needed, bug fix
Change-Id: I3dcb0b8ff0aa77bf3183a926889d0131b17bcaa4