MB-100: disable warnings on deprecated functions for gen_smtp

I.e. for R16B01

Change-Id: I04224177b56afc2885bab8d7be1e8dd66effd7dc
Reviewed-on: http://review.couchbase.org/27558
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>