clearing out old plugin entity/object types

i notice that traces of some plugins i have installed and then uninstalled remain in the database and appear in some places in the site; such as the account statistics panel in user settings..

e.g. izap_videos - count - remains in the statistics panel even though i have uninstalled it.

does the garbage collector clear these details out? is it perhaps not running on my site?

or is there another way to do this?

(elgg 1.8.8)
thanks