Remove obsolete TODO. (#3827)

lib/src/exceptions.dart

diff --git a/lib/src/exceptions.dart b/lib/src/exceptions.dart
index c70c53d..f715b10 100644
--- a/lib/src/exceptions.dart
+++ b/lib/src/exceptions.dart
@@ -116,8 +116,6 @@
 ///
 /// This includes both [ApplicationException] and any dart:io errors.
 bool isUserFacingException(error) {
-  // TODO(nweiz): unify this list with _userFacingExceptions when issue 5897 is
-  // fixed.
   return error is ApplicationException ||
       error is AnalyzerErrorGroup ||
       error is IsolateSpawnException ||