Remove dead code left over from NITB split

There still is a lot of dead code that we inherited from the NITB
days, let's remove more of it.

libtrau will be re-introduced as part of osmo-mgw later.

Change-Id: I8e0af56a158f25a4f1384d667c03eb20e72df5b8
diff --git a/include/osmocom/bsc/ipaccess.h b/include/osmocom/bsc/ipaccess.h
index 82e89c2..3d0f612 100644
--- a/include/osmocom/bsc/ipaccess.h
+++ b/include/osmocom/bsc/ipaccess.h
@@ -2,11 +2,13 @@
 #define _IPACCESS_H
 
 #include <osmocom/abis/e1_input.h>
-#include "gsm_subscriber.h"
 #include <osmocom/core/linuxlist.h>
 #include <osmocom/gsm/protocol/ipaccess.h>
 #include <osmocom/gsm/protocol/gsm_23_003.h>
 
+struct gsm_bts;
+struct gsm_bts_trx;
+
 struct ipac_msgt_sccp_state {
 	uint8_t	src_ref[3];
 	uint8_t	dst_ref[3];