Cleanup IPinnedStackController and IPinnedStackListener 1/N

Remove the IPinnedStackController aidl interface. The only method was
left in IPinnedStackController is the getDisplayRotation and used only
by PipTouchHandler. Switched that over to Context.getDisplay#getRotation

Video: http://rcll/aaaaaabFQoRHlzixHdtY/bO1xoqLNemseqmk603y9us
Bug: 174702196
Test: verify the original bug (b/36879891) is still fixed, see video
Test: atest PinnedStackTests \
            WMShellUnitTests
Change-Id: I65814b25ed9a1fb28dad4d6eae88b949efc15e3c