Fix SecurityException while accessing Slice Uris

- There is SecurityException when accessing Slice Uris which are not in
  Settings app.
- Rollback to the original mechanism, remove an unused latch, and
  register a trivial callback

Fixes: 159195420
Test: robotest
Change-Id: Ice2cf5f928b0e6d0367bcc41c3912526e8f7bd7f