Remove Lollipop support for InCallUI

This CL removes support for running dialer on Android L MR1.
The change allows us to switch from the system SDK to the public SDK.

This is useful for the following reasons:
  - makes it easier to switch to gradle
  - makes it easier to migrate GoogleDialer to google3
  - reduces maintenance overhead for unused code

Currently there's no plan to release Dialer on Lollipop. If or when
we decide to support Lollipop we can consider switching back to the
system SDK and restoring the comapatiblity code.

Bug: 26676586
Change-Id: Idac9e6e19f1d21c9261c1b0d0ff3e3ca4aab980b
14 files changed