Fix issue where system rings even if default dialer can play ringtone.

A few issues:
1. The InCallController wasn't actually tracking which UI was bound.
This turns out to be easy enough to determine using the list of
mInCallServices.
2. The static DefaultDialerManager.getDefaultDialerApplication method
was being used to get the default dialer, where there is already a local
instance of default dialer manager in InCallController.

Bug: 116871247
Test: Install dialer which is able to support ringing; verify system no
longer rings.
Test: Install dialer which does not support ringing; verify system rings.

Change-Id: I82998a318587061d930e07f1f6c132c5b31743b4