CBQE-1129: remove worker atop collection

Stat collection is now being handled entirely by cbmonitor.

Change-Id: Ic7f60bbbe3806fc43bd46dafb4537f9d06c63543
Reviewed-on: http://review.couchbase.org/25176
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Tommie McAfee <tommie@couchbase.com>