Drop (unused) dtrace support

Change-Id: I18bef829a77bb7f71bcc1ab8c2575f8f9a1e1805
Reviewed-on: http://review.couchbase.org/27002
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Michael Wiederhold <mike@couchbase.com>