removed Action trigger from worker ModeHookError

This patches a bug in the uniter which can result in ModeHookError being
cleared by a successful Action run on the impacted unit.  Actions can no
longer be run in ModeHookError.

This will be resolved after the Context refactor on worker.
Merge pull request #730 from binary132/actions-modehookerror-fix

removed Action trigger from worker ModeHookError

This patches a bug in the uniter which can result in ModeHookError being
cleared by a successful Action run on the impacted unit.  Actions can no
longer be run in ModeHookError.

This will be resolved after the Context refactor on worker.