Replace CallServiceSelectors with Subscriptions (3/3)

Remove CallServiceSelectors and replace them with comprehensive
support for Subscriptions as the means of selecting ways of making
phone calls. After this change, a ConnectionService is not a
semantically meaningful "way of making a call" -- it's more like the
mechanism whereby the Android system communicates with a 3rd party
process to ask for phone services. We anticipate each process having
only one ConnectionService.

Change-Id: I251c0b6f4106104d945b3723fa4da1081a06b8cd
12 files changed