Rewrite the const constructor negative tests into a single multi test.

tests/language/src/ConstConstructorSyntaxTest.dart

+// Copyright (c) 2012, 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.
+
+main() {
+  var c0 = const C0(); /// 01: compile-time error
+  var i0 = const I0(); /// 02: compile-time error
+  var c1 = const C1();
+  var c2 = const C2(); /// 03: compile-time error
+}
+
+interface I0 default C0 {
+  I0();
+}
+
+class C0 implements I0 {
+  C0();
+}
+
+class C1 {
+  const C1();
+  var modifiable; /// 04: compile-time error
+}
+
+class C2 {
+  C2();
+}