Remove local libgsupclient; Use libosmo-gsup-client from osmo-hlr

osmo-hlr has recently (as of Change-Id
Iad227bb477d64da30dd6bfbbe1bd0c0a55be9474) a working shared library
implementation of libosmo-gsup-client.

We can remove the local implementation in osmo-sgsn and use the
system-installed shared library instead.

Change-Id: I6f542945403cf2e3ddac419186b09ec0e2d43b69
diff --git a/src/gprs/sgsn_vty.c b/src/gprs/sgsn_vty.c
index 72a310b..f57a2b9 100644
--- a/src/gprs/sgsn_vty.c
+++ b/src/gprs/sgsn_vty.c
@@ -37,7 +37,7 @@
 #include <osmocom/sgsn/gprs_gmm.h>
 #include <osmocom/sgsn/gprs_sgsn.h>
 #include <osmocom/sgsn/vty.h>
-#include <osmocom/sgsn/gsup_client.h>
+#include <osmocom/gsupclient/gsup_client.h>
 
 #include <osmocom/vty/command.h>
 #include <osmocom/vty/vty.h>