Clear binder calling identity before calling callback

This change clears calling identities before the
onSubscriptionsChangedListener.onSubscriptionsChanged() callback is
made.

Bug: 193731920
Test: atest TelephonyRegistryManagerTest
Original-Change: https://android-review.googlesource.com/1767051
Merged-In: I21f14e40a05f76346eb90b8f36608b4d6bdf1a29
Change-Id: I21f14e40a05f76346eb90b8f36608b4d6bdf1a29