Remove deprecated Strings class.

sdk/lib/_internal/dartdoc/lib/src/dartdoc/utils.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 dartdoc;
 
 // Generic utility functions.
 
 /** Turns [name] into something that's safe to use as a file name. */
 String sanitize(String name) => name.replaceAll(':', '_').replaceAll('/', '_');
@@ skipping 50 matching lines @@
   return elements;
 }
 
 /**
  * Joins [items] into a single, comma-separated string using [conjunction].
  * E.g. `['A', 'B', 'C']` becomes `"A, B, and C"`.
  */
 String joinWithCommas(List<String> items, [String conjunction = 'and']) {
   if (items.length == 1) return items[0];
   if (items.length == 2) return "${items[0]} $conjunction ${items[1]}";
-  return '${Strings.join(items.getRange(0, items.length - 1), ', ')}'
+  return '${items.getRange(0, items.length - 1).join(', ')}'
     ', $conjunction ${items[items.length - 1]}';
 }
 
 void writeString(File file, String text) {
   var randomAccessFile = file.openSync(FileMode.WRITE);
   randomAccessFile.writeStringSync(text);
   randomAccessFile.closeSync();
 }