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/debian/control b/debian/control
index 8e34dbe..9594a08 100644
--- a/debian/control
+++ b/debian/control
@@ -19,7 +19,8 @@
                libosmo-ranap-dev,
                libosmo-sccp-dev,
                libosmo-sigtran-dev,
-               libosmo-netif-dev
+               libosmo-netif-dev,
+               libosmo-gsup-client-dev
 Standards-Version: 3.9.8
 Vcs-Git: git://git.osmocom.org/osmo-sgsn.git
 Vcs-Browser: https://git.osmocom.org/osmo-sgsn