Fix memory leak in widgetsgallery.
Fix memory leak in widgetsgallery.

RevBy: Adria Yanes
Details:
Do not try to manually delete the rows in the model and just let
clear() get rid of them.

nemomobile-graveyard/libmeegotouch,nemomobile-graveyard/libmeegotouch,nemomobile-graveyard/libmeegotouch,nemomobile-graveyard/libmeegotouch,nemomobile-graveyard/libmeegotouch,nemomobile-graveyard/libmeegotouch