InCallUI: Flip to Mute/Reject Call cleanup: fix ITelephony access

Using reflection to access ITelephony is a strange idea

Change-Id: Ia2ebebb102fc4b55983d1e7f7fd30f426c6f8ac7
[1/2] InCallUI: unify flip action handler

We cannot share the code since DeskClock is only using
the app API but we can at least share the file.

PS2
NPE derp

Change-Id: I9f9c3431d74330a2d46ffa4965483cad24336a52