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/calls-history-box.c

@@ -94,7 +94,7 @@ delete_call_cb (CallsCallRecord *record,
 
   g_return_if_fail (CALLS_IS_CALL_RECORD (record));
 
-  ok = calls_find_in_store (self->model,
+  ok = calls_find_in_model (self->model,
                             record,
                             &position);