Don't initialize raftable if use_raftable is false.

Author: kvap

contrib/mmts/multimaster.c

@@ -2262,7 +2262,8 @@ _PG_init(void)
 
     BgwPoolStart(MtmWorkers, MtmPoolConstructor);
 
-	MtmRaftableInitialize();
+	if (MtmUseRaftable)
+		MtmRaftableInitialize();
 	MtmArbiterInitialize();
 
 	/*