entc/gen: delete removal edges from mutation (#1654)

* Remove Edge IDs from internal Mutation state

* Update template gen

* Update integration tests

* Update examples

examples/fs/ent/mutation.go

@@ -300,6 +300,7 @@ func (m *FileMutation) RemoveChildIDs(ids ...int) {
 		m.removedchildren = make(map[int]struct{})
 	}
 	for i := range ids {
+		delete(m.children, ids[i])
 		m.removedchildren[ids[i]] = struct{}{}
 	}
 }