Clear calling identify before using package manager in TelecomServiceImpl.

Some calls are made to getPackageUid from the caller's identity, which
causes a crash for apps calling from private space since it is a cross
user request.

Flag: com.android.server.telecom.flags.allow_system_apps_resolve_voip_calls
Test: Install test app in private space and verify it no longer crashes when
calling TelecomManager.endCall
Fixes: 399623655

Change-Id: I09174e65e2a2d146d36c803a229bee7cee6cf258