Kill fast warmup settings.

Fast warmup support has never been implemented in ns_server.

Change-Id: Ic630e56052068b29b6fb77b59b80f98cd66c7f2b
Reviewed-on: http://review.couchbase.org/42087
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>