clutter/actor: Mark implicit transitions as remove-on-complete
Implicit transitions had a referenced taken while emitting the completion signals, but said reference would only be released if it was had remove-on-complete set to TRUE.
Change this to instead remove the 'is_implicit' state and mark all implicit transitions as remove-on-complete. This fixes a ClutterPropertyTransition leak in gnome-shell triggered by e.g. showing / hiding menus.
Fixes: gnome-shell#1740 (closed)