protected void sendError(ChannelHandlerContext ctx, HttpResponseStatus status) {
      sendError(ctx, "", status);
    }
Unregister a specific dag

This method and registerDag must be synchronized externally to prevent races in shuffle token registration/unregistration

@param dir
@param applicationIdString
@param dagIdentifier
llap-server/src/java/org/apache/hadoop/hive/llap/shufflehandler/ShuffleHandler.java