MB-11427 Don't advertise datatype support.

Datatype support was disabled in memcached:
http://review.couchbase.org/38228

Change-Id: I9d548e08ea2a8ff70630e11b46aed2737ab79ff3
Reviewed-on: http://review.couchbase.org/38273
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>