MB-100: removed wrong doc comment on top of mb_master

Change-Id: I685eab3e37ccc40293861d38b6152c8c821421ef
Reviewed-on: http://review.couchbase.org/30123
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>