transaction.h: use #pragma once as include guard

Change-Id: I52787120d5ec59897329d28eab28e0fda3d0f44f

include/osmocom/msc/transaction.h

@@ -1,5 +1,4 @@
-#ifndef _TRANSACT_H
-#define _TRANSACT_H
+#pragma once
 
 #include <osmocom/msc/gsm_data.h>
 #include <osmocom/msc/gsm_subscriber.h>
@@ -117,5 +116,3 @@ int trans_assign_trans_id(const struct gsm_network *net, const struct vlr_subscr
 			  uint8_t protocol);
 struct gsm_trans *trans_has_conn(const struct ran_conn *conn);
 void trans_conn_closed(const struct ran_conn *conn);
-
-#endif