MB-11969 Remove detailed key stats

Change-Id: If4bf7359f5a5fad31e23174f192f0a99f94ab11b
Reviewed-on: http://review.couchbase.org/40649
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Jim Walker <jim@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>