FolderView and AllView currently check if the item is
present in the BaseAppView._items map, in order to avoid
adding the same icon multiple times.
Now that BaseAppView._loadGrid() has a different role
-- it returns a list with all app icons, and BaseAppView
diffs with the current list of app icons -- checking the
BaseAppView._items map is wrong.
Make sure there are no duplicated items in the temporary
array returned by all _loadGrid() implementations. Remove
the now unused BaseAppView.hasItem() method.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/645
9da49606f7