moved xdc_replication state definition out of .hrl and into .erl

Change-Id: If928d4a23f2e9c7487cace733c74326d546ad37f
Reviewed-on: http://review.couchbase.org/40089
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>