Revert "Allowing `e` of any type in `void f(...) => e` in the analyzer."

tests/language/void_block_return_test.dart

-// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// Testing that a void block function is not allowed to `return e`
-// where `e` is non-void.
-
-void foo() {
-  return 42; //# 00: static type warning
-}
-
-main() {
-  foo();
-}