Remove unused imports.

pkg/front_end/lib/src/fasta/scanner/token.dart

Index: pkg/front_end/lib/src/fasta/scanner/token.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/token.dart b/pkg/front_end/lib/src/fasta/scanner/token.dart
index 11fe838eff1201a5ae8687eb4fedc7b61db6010f..44aa93d976cf8a3e86797bd2088ef10fac52e0bb 100644
--- a/pkg/front_end/lib/src/fasta/scanner/token.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/token.dart
@@ -4,12 +4,6 @@
 
 library fasta.scanner.token;
 
-import 'dart:collection' show
-    HashSet;
-
-import 'dart:convert' show
-    UTF8;
-
 import 'keyword.dart' show
     Keyword;