Remove deprecated 'str' getter on Match.

runtime/lib/regexp_patch.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.
 
 patch class RegExp {
   /* patch */ factory RegExp(String source,
                              {bool multiLine: false,
                               bool caseSensitive: true}) {
     return new _JSSyntaxRegExp(source,
                                multiLine: multiLine,
@@ skipping 37 matching lines @@
     for (int i = 0; i < groupsSpec.length; i++) {
       groupsList[i] = group(groupsSpec[i]);
     }
     return groupsList;
   }
 
   int get groupCount => _regexp._groupCount;
 
   Pattern get pattern => _regexp;
 
-  // TODO(12843): Remove when grace period is over.
-  String get str => input;
-
   final RegExp _regexp;
   final String input;
   final List<int> _match;
   static const int _MATCH_PAIR = 2;
 }
 
 
 class _JSSyntaxRegExp implements RegExp {
   factory _JSSyntaxRegExp(
       String pattern,
@@ skipping 86 matching lines @@
     var match = _re._ExecuteMatch(_str, nextIndex);
     if (match == null) {
       _current = null;
       _re = null;
       return false;
     }
     _current = new _JSRegExpMatch(_re, _str, match);
     return true;
   }
 }