Switch on null-aware operators by default in analyzer.

tests/language/super_conditional_operator_test.dart

 // Copyright (c) 2015, 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.
 
 // Verify that the ?. operator cannot be used with "super".
 
-// SharedOptions=--enable-null-aware-operators
-
 class B {
   B();
   B.namedConstructor();
   var field = 1;
   method() => 1;
 }
 
 class C extends B {
   C()
     : super?.namedConstructor() /// 01: compile-time error
@@ skipping 16 matching lines @@
     ~super?.method(); /// 15: compile-time error
     !super?.method(); /// 16: compile-time error
     --super?.method(); /// 17: compile-time error
     ++super?.method(); /// 18: compile-time error
   }
 }
 
 main() {
   new C().test();
 }