rework /debian support to match new osmo-sgsn

Remove old leftover from split of osmo-sgsn out of openbsc.

Change-Id: Ic0135a1118a115e8f053154e280f60674390f43a
diff --git a/debian/osmo-gbproxy.install b/debian/osmo-gbproxy.install
new file mode 100644
index 0000000..62ebe2a
--- /dev/null
+++ b/debian/osmo-gbproxy.install
@@ -0,0 +1,2 @@
+usr/bin/osmo-gbproxy
+usr/share/doc/openbsc/examples/osmo-gbproxy