Mock TelephonyManager in NotificationManagerService tests.

This prevents NMSTest failure due to too many TelephonyService
listeners. (Because NMS never shuts down in normal use, it doesn't
unregister its listeners.)

Bug: 152241061
Test: atest NotificationManagerServiceTest RoleObserverTest BuzzBeepBlinkTest

Change-Id: Ia5988a194aff2e5a83cf15fcd422c063a3ca14f1