Remove dependency of EmergencyCallbackModeExitDialog

Change EmergencyCallbackModeExitDialog to use the activity result code
to represent the user choice.

RESULT_OK mean the user click "yes" and exit the Emergency Callback
Mode, otherwise, RESULT_CANCELED will be returned.

This change allows the MobileNetworkSettings decouple from
EmergencyCallbackModeExitDialog.

Bug: 111453847
Test: Build & manual test
Change-Id: I4c2a4843a95858c16e45f13b4f38dc6def3bacf0
2 files changed