Initialize Dependency with the Application when Dagger starts.

Dependency is no longer a subclass of SystemUI. It gets initialized
directly as part of the application, just like the rest of Dagger.
It was an awkward implementation of SystemUI anyways.

Bug: 137324767
Change-Id: Icf49e9262e8c0710210a8bc0231c4d16396ffdf3
Test: atest SystemUITests