Switch from ITransactionCompletedListener to IBinder keys

IBinder remains consistent across multiple transactions when passed
cross-process to SF.  However, interface_cast'ing it to an
ITransactionCompletedListener results in different underlying objects.
Switch to using IBinder as the keys for listener callbacks.

Bug: 139731321
Test: build, boot, SurfaceFlinger_test
Change-Id: I9bea76664087020eb43ceec258b5ecede0faaea5