Remove package imports from itself.

pkg/front_end/lib/src/fasta/quote.dart

 // Copyright (c) 2016, 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.quote;
 
 import 'errors.dart' show inputError, internalError;
 
-import 'package:front_end/src/fasta/scanner/characters.dart'
+import 'scanner/characters.dart'
     show
         $BACKSLASH,
         $BS,
         $CLOSE_CURLY_BRACKET,
         $CR,
         $FF,
         $LF,
         $OPEN_CURLY_BRACKET,
         $SPACE,
         $TAB,
@@ skipping 210 matching lines @@
         }
       } else {
         // Nothing, escaped character is passed through;
       }
       if (code > 0x10FFFF) return error(i, invalidCodePoint);
     }
     result[resultOffset++] = code;
   }
   return new String.fromCharCodes(result, 0, resultOffset);
 }