Remove deprecated Strings class.

sdk/lib/uri/helpers.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.
 
 part of dart.uri;
 
 String merge(String base, String reference) {
   if (base == "") return "/$reference";
   return "${base.substring(0, base.lastIndexOf("/") + 1)}$reference";
 }
 
 String removeDotSegments(String path) {
   List<String> output = [];
   bool appendSlash = false;
   for (String segment in path.split("/")) {
     appendSlash = false;
     if (segment == "..") {
       if (!output.isEmpty &&
           ((output.length != 1) || (output[0] != ""))) output.removeLast();
       appendSlash = true;
     } else if ("." == segment) {
       appendSlash = true;
     } else {
       output.add(segment);
     }
   }
   if (appendSlash) output.add("");
-  return Strings.join(output, "/");
+  return output.join("/");
 }