Merge "TelephonyBackupAgentTest: Clean up after ourselves." am: fa7699e0f7

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/providers/TelephonyProvider/+/12588545

Change-Id: Ia79a6e4d009b79c7f0ceea1fa5309bfbacd1fd93