MB-11435: removed unnecessary xdcr logging from hot path

Change-Id: Ib587a2e22d867f901d322fa960d99ddf18af146a
Reviewed-on: http://review.couchbase.org/39189
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>