Remove an extra period in code comment

Author: Junwang Zhao
Discussion: https://postgr.es/m/CAEG8a3L9GgfKc+XT+NMHPY7atAOVYqjUqKEFQKhcPHFYRW=PuQ@mail.gmail.com

Author: Richard Guo

src/backend/storage/ipc/procarray.c

@@ -185,7 +185,7 @@ typedef struct ComputeXidHorizonsResult
 	FullTransactionId latest_completed;
 
 	/*
-	 * The same for procArray->replication_slot_xmin and.
+	 * The same for procArray->replication_slot_xmin and
 	 * procArray->replication_slot_catalog_xmin.
 	 */
 	TransactionId slot_xmin;