delete obsolete scanner roundtrip test

pkg/front_end/test/token_test.dart

 // Copyright (c) 2017, 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.
 
 import 'package:front_end/src/fasta/scanner/string_scanner.dart';
 import 'package:front_end/src/fasta/scanner/token.dart' as fasta;
 import 'package:front_end/src/scanner/token.dart';
+import 'package:front_end/src/scanner/errors.dart' as analyzer;
 import 'package:front_end/src/scanner/reader.dart' as analyzer;
+import 'package:front_end/src/scanner/scanner.dart' as analyzer;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
-import 'scanner_roundtrip_test.dart' show TestScanner;
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TokenTest);
   });
 }
 
 /// Assert that fasta PrecedenceInfo implements analyzer TokenType.
 @reflectiveTest
 class TokenTest {
@@ skipping 179 matching lines @@
     // General tokens
     token = token.next;
     expect(token.lexeme, '&');
     expect(token.value(), '&');
     // String tokens
     token = token.next;
     expect(token.lexeme, '"home"');
     expect(token.value(), '"home"');
   }
 }
+
+class TestScanner extends analyzer.Scanner {
+  TestScanner(analyzer.CharacterReader reader) : super.create(reader);
+
+  @override
+  void reportError(
+      analyzer.ScannerErrorCode errorCode, int offset, List<Object> arguments) {
+    fail('Unexpected error $errorCode while scanning offset $offset\n'
+        '   arguments: $arguments');
+  }
+}