Fixup clean-all, clean-all-async and invalidate dependencies.

In the wake of Goal.dependencies no longer being used for scheduling,
clean-all and invalidate no longer properly depend on ng-killall.

Testing Done:
Ad-hoc:
$ for goal in clean-all clean-all-async invalidate ng-killall; do PANTS_DEV=1 ./pants goal $goal -e 2>/dev/null | grep $goal | grep "\["; done
clean-all [ng-killall->NailgunKillall, invalidate->Invalidator, clean-all->Cleaner]
clean-all-async [ng-killall->NailgunKillall, invalidate->Invalidator, clean-all-async->AsyncCleaner]
invalidate [ng-killall->NailgunKillall, invalidate->Invalidator]
ng-killall [ng-killall->NailgunKillall]

Bugs closed: 319

Reviewed at https://rbcommons.com/s/twitter/r/638/