contact-search-dialog: fix GtkSizeGroup leak
contact-search-dialog: fix GtkSizeGroup leak

GtkSizeGroup objects are referenced by each widget in the size group,
so once you have added all widgets to a GtkSizeGroup, you can drop the
initial reference to the size group with g_object_unref().

https://bugzilla.gnome.org/show_bug.cgi?id=685652

GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,Distrotech/telepathy-account-widgets