remove unused KeywordToken import

pkg/front_end/lib/src/fasta/scanner/abstract_scanner.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.
 
 library fasta.scanner.abstract_scanner;
 
 import 'dart:collection' show ListMixin;
 
 import 'dart:typed_data' show Uint16List, Uint32List;
 
 import '../scanner.dart'
     show ErrorToken, Scanner, buildUnexpectedCharacterToken;
 
 import 'error_token.dart' show UnmatchedToken, UnterminatedToken;
 
 import 'keyword.dart' show KeywordState, Keyword;
 
 import 'precedence.dart';
 
-import 'token.dart' show BeginGroupToken, KeywordToken, SymbolToken, Token;
+import 'token.dart' show BeginGroupToken, SymbolToken, Token;
 
 import 'token_constants.dart';
 
 import 'characters.dart';
 
 abstract class AbstractScanner implements Scanner {
   final bool includeComments;
 
   /**
    * The string offset for the next token that will be created.
@@ skipping 1210 matching lines @@
       switchToUint32(newLength);
     }
   }
 
   void switchToUint32(int newLength) {
     final newArray = new Uint32List(newLength);
     newArray.setRange(0, arrayLength, array);
     array = newArray;
   }
 }