Don't set max_txn_size when creating a couchbase bucket

This parameter doesn't have any use in ep-engine anymore and will
be removed.

Change-Id: I637b247f04a7f77ea83ff2696daf8a321787397e
Reviewed-on: http://review.couchbase.org/34387
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>