Cleanup: get rid of getCurrentCall() method.

The only caller was the vibration code, which only used it when the call
is picked up. As a picked up call is always the foreground one, we can
safely just use that.

Change-Id: Id3e4f9d3738bfe72387899802b89202bfef61646
Fix 'vibrate outgoing' behaviour.

Change-Id: I08d05dcf03074af73e9fcf9a2f9788cd46b27833