Remove RejectedExecutionHandler for long/short compaction thread pools

As disscussed in https://github.com/apache/hbase/pull/4725

actually the max size of StealJobQueue is bouded by the VM limit of an array, and the OOM exception occurs before the rejection handler. So StealJobQueue is equivalent to be unbounded. I think the RejectionHandler may bring some confusions and make the codes a little puzzle.