Some small bug fixes in NUI.

 - Never show the dialpad chooser in MainActivity.
 - If the call log changed while dialer was in the background, it would trigger
 the content observer to fetch the new info, which would request it's parent
 that wasn't there. Now we register/unregister them in onResume/onPause. This
 is safe to do because we force refresh the data onResume anyways, so any
 changes will still be shown.

Bug: 73972084,73975555,73995512
Test: manual
PiperOrigin-RevId: 187407058
Change-Id: Iae86dabbcb852398bb2b9df4627e234261ab8030