Update ActivityEmbedding split open/close animation adapter for Shell

Make sure the open/close a pair of activities act as one.
Cleanup unused adapter that was introduced for scaling animation, which
is replaced with x coordinate animation in T.

Bug: 19847347
Test: manually verify the animation with Shell transition
Change-Id: I5a34c2cf163f2a330e4c8111c16f8125bd5c2db5