Revert "Update all Angular libs (run update_all.sh)."

third_party/pkg/di/lib/src/error_helper.dart

-library di.error_helper;
-
-import 'package:di/di.dart';
-import 'package:di/src/base_injector.dart';
-
-String error(ResolutionContext resolving, message, [Key appendDependency]) {
-  if (appendDependency != null) {
-    resolving = new ResolutionContext(resolving.depth + 1, appendDependency, resolving);
-  }
-
-  String graph = resolvedTypes(resolving).reversed.join(' -> ');
-
-  return '$message (resolving $graph)';
-}
-
-List<Key> resolvedTypes(ResolutionContext resolving) {
-  List resolved = [];
-  while (resolving.depth != 0) {
-    resolved.add(resolving.key);
-    resolving = resolving.parent;
-  }
-  return resolved;
-}