Dialer: Start converting to AndroidX [10/x]

* androidx.annotation being "easy" since it has no dependencies that
  interfere with the remaining legacy libs
* Removed a few unused imports along the way when I saw them
* Don't fight AS when it wants to import com.android.dialer.R - it
  probably has to do with my stupid gradle file and I can't figure out
  why it wants it - just that we can still build and use the app

Change-Id: Ib69b6f434a74af8d4d9ae4edfcdfb5b153b9d42c