todo vanished (#2019)

Author: Brian Chen

packages/firestore/src/util/error.ts

@@ -23,7 +23,6 @@ import * as firestore from '@firebase/firestore-types';
  */
 export type Code = firestore.FirestoreErrorCode;
 
-// TODO(mcg): Change to a string enum once we've upgraded to typescript 2.4.
 export const Code = {
   // Causes are copied from:
   // https://github.com/grpc/grpc/blob/bceec94ea4fc5f0085d81235d8e1c06798dc341a/include/grpc%2B%2B/impl/codegen/status_code_enum.h