MXS-1209: added SELECT @@GLOBAL.gtid_domain_id for Master GTID registration

Master GTID registration: added first step: support for “SELECT
@@GLOBAL.gtid_domain_id”

server/modules/routing/binlogrouter/blr.c

@@ -373,9 +373,6 @@ createInstance(SERVICE *service, char **options)
     /* Encryption CTX */
     inst->encryption_ctx = NULL;
 
-    /* MariaDB GTID repo init val */
-    inst->gtid_repo = NULL;
-
     /* Set router uuid */
     inst->uuid = config_copy_string(params, "uuid");