schema/edge: allow setting immutable edges (#2876)

examples/start/ent/mutation.go

@@ -423,8 +423,6 @@ func (m *CarMutation) RemovedEdges() []string {
 // RemovedIDs returns all IDs (to other nodes) that were removed for the edge with
 // the given name in this mutation.
 func (m *CarMutation) RemovedIDs(name string) []ent.Value {
-	switch name {
-	}
 	return nil
 }