Revert "Avoid warning when using `return;` from sync* and async* functions."

tests/language/async_return_types_test.dart

Index: tests/language/async_return_types_test.dart
diff --git a/tests/language/async_return_types_test.dart b/tests/language/async_return_types_test.dart
index 1134e25b0038c1d9caf25cac9229d5972427410d..83eb9a8d992f441ece1e655ef2cece1056798739 100644
--- a/tests/language/async_return_types_test.dart
+++ b/tests/language/async_return_types_test.dart
@@ -40,23 +40,6 @@ foo7() async {
   return new Future<int>.value(3);
 }
 
-
-Iterable<int> foo8() sync* {
-  yield 1;
-  // Can only have valueless return in sync* functions.
-  return
-      8 /// return_value_sync_star: compile-time error
-       ;
-}
-
-Stream<int> foo9() async* {
-  yield 1;
-  // Can only have valueless return in async* functions.
-  return
-      8 /// return_value_sync_star: compile-time error
-       ;
-}
-
 test() async {
   Expect.equals(3, await foo1());
   Expect.equals(3, await foo2());
@@ -65,8 +48,6 @@ test() async {
   Expect.equals(3, await foo5());
   Expect.equals(3, await await foo6());
   Expect.equals(3, await await foo7());
-  Expect.listEquals([1], foo8().toList());
-  Expect.listEquals([1], await foo9().toList());
 }
 
 main() {