Remove unintentional dependency on analysis_server

pkg/analysis_server/lib/src/services/refactoring/naming_conventions.dart

 // Copyright (c) 2014, 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 services.src.refactoring.naming_conventions;
-
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/correction/strings.dart';
+import 'package:analyzer_plugin/src/utilities/string_utilities.dart';
 import 'package:front_end/src/scanner/token.dart' show Keyword;
 
 /**
  * Returns the [RefactoringStatus] with severity:
  *   OK if the name is valid;
  *   WARNING if the name is discouraged;
  *   FATAL if the name is illegal.
  */
 RefactoringStatus validateClassName(String name) {
   return _validateUpperCamelCase(name, "Class");
@@ skipping 236 matching lines @@
   }
   // does not start with upper case
   if (!isUpperCase(identifier.codeUnitAt(0))) {
     // By convention, class names usually start with an uppercase letter
     String message = "$desc should start with an uppercase letter.";
     return new RefactoringStatus.warning(message);
   }
   // OK
   return new RefactoringStatus();
 }