This task pays of some technical debt that was added to support a risky change.
In solving T206274 we dropped use of the ChangesListSpecialPageQuery hook.
The fix went into 1.32.0-wmf.26 which is now live on all wikis.
A feature flag was added to allow us to roll back in the event of a problem, but no problems have been encountered.
- MFWatchlistRunsChangesListSpecialPageQuery is removed from extension.json
- SpecialMobileWatchlist doesn't run ChangesListSpecialPageQuery hook