delete obsolete scanner roundtrip test

pkg/front_end/test/token_test.dart

Index: pkg/front_end/test/token_test.dart
diff --git a/pkg/front_end/test/token_test.dart b/pkg/front_end/test/token_test.dart
index cf2a4c19812372f9187a40073d5d4049ce779f51..84150964690d5fdc2e50b67b85109b0b39a04aed 100644
--- a/pkg/front_end/test/token_test.dart
+++ b/pkg/front_end/test/token_test.dart
@@ -5,10 +5,11 @@
 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(() {
@@ -208,3 +209,14 @@ class Foo {
     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');
+  }
+}