Remove flag for enabling null-aware operators. They are now on by default.

pkg/compiler/lib/src/apiimpl.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.
 
 library leg_apiimpl;
 
 import 'dart:async';
 import 'dart:convert';
 
 import '../compiler.dart' as api;
@@ skipping 86 matching lines @@
                 forceIncrementalSupport ||
                 hasOption(options, '--incremental-support'),
             suppressWarnings: hasOption(options, '--suppress-warnings'),
             fatalWarnings: hasOption(options, '--fatal-warnings'),
             enableExperimentalMirrors:
                 hasOption(options, '--enable-experimental-mirrors'),
             generateCodeWithCompileTimeErrors:
                 hasOption(options, '--generate-code-with-compile-time-errors'),
             testMode: hasOption(options, '--test-mode'),
             allowNativeExtensions:
-                hasOption(options, '--allow-native-extensions'),
-            enableNullAwareOperators:
-                hasOption(options, '--enable-null-aware-operators')) {
+                hasOption(options, '--allow-native-extensions')) {
     tasks.addAll([
         userHandlerTask = new leg.GenericTask('Diagnostic handler', this),
         userProviderTask = new leg.GenericTask('Input provider', this),
         userPackagesDiscoveryTask =
             new leg.GenericTask('Package discovery', this),
     ]);
     if (libraryRoot == null) {
       throw new ArgumentError("[libraryRoot] is null.");
     }
     if (!libraryRoot.path.endsWith("/")) {
@@ skipping 351 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }