util: Rename function to calls_find_in_model() and adjust documentation

Since it works for GListModel rename it appropriately.

It used to provide an inline implementation for g_list_store_find()
behind a glib version guard, but we bumped minimum version in
cfd3c2a7fe
so the docstring was updated and made more succinct.

src/util.h

@@ -119,7 +119,7 @@ gboolean    calls_date_time_is_same_year (GDateTime  *a,
                                            GDateTime *b);
 gboolean    calls_number_is_ussd         (const char *number);
 
-gboolean    calls_find_in_store (GListModel *list,
+gboolean    calls_find_in_model (GListModel *list,
                                   gpointer   item,
                                   guint     *position);