Remove legacy syntax support for library import

tests/standalone/package/packages/lib1.dart

Index: tests/standalone/package/packages/lib1.dart
===================================================================
--- tests/standalone/package/packages/lib1.dart	(revision 20447)
+++ tests/standalone/package/packages/lib1.dart	(working copy)
@@ -2,10 +2,10 @@
 // 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('lib1');
+library lib1;
 
-#import('package:shared.dart');
-#import('package:lib2/lib2.dart');
+import 'package:shared.dart';
+import 'package:lib2/lib2.dart';
 
 void lib1() {
   output += '|lib1';