Simplify watcher count display in Pending Changes table

- Deleted the 'pendingchanges-watched' message key and directly
  displayed the number of active watchers.
- Updated the column heading from 'Watching' to 'Active Watchers' for
  clarity.

Bug: T372203
Change-Id: I4b5d121718374429150b3c9648e3901339dbfdd5
3 files changed