Remove useless warning about empty response body for request with files

lib/helpers/api_helper.dart

@@ -67,8 +67,6 @@ class APIHelper {
   }
 
   /// Same as exec, but also allows to send files
-  ///
-  /// Warning ! Currently the response body to such requests is always null !
   Future<APIResponse> execWithFiles(APIRequest request) async {
     return await exec(request, multipart: true);
   }