Merge "Allow the System UID to unregister ConnDiags CBs." am: fcb4e29a9c am: a8f74e302c am: c5c47be1b9

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1515688

Change-Id: I123cfe5c1ea8d6f466bf831e87a8a11f8cf12e25