Remove osmo-sgsn relics

* include/osmocom/sgsn -> gbproxy
* (unused) tests specific to osmo-sgsn

Change-Id: I3704760e8936bdd005a3f73727de5f2b3e8774a0
diff --git a/src/gb_proxy_vty.c b/src/gb_proxy_vty.c
index 3a52e32..f48a6db 100644
--- a/src/gb_proxy_vty.c
+++ b/src/gb_proxy_vty.c
@@ -39,7 +39,7 @@
 #include <osmocom/gsm/gsm48.h>
 
 #include "debug.h"
-#include <osmocom/sgsn/gb_proxy.h>
+#include <osmocom/gbproxy/gb_proxy.h>
 
 #include <osmocom/vty/command.h>
 #include <osmocom/vty/logging.h>