dropped vbs_replicating stat

Change-Id: I2494435a0d48760684c0304e3664e912878cdf20
Reviewed-on: http://review.couchbase.org/40091
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>