jenkins: fix build: osmo-mgw from master, not pre_release

pre_release is gone, we need to build from master now.

Change-Id: I86a50c523ab04d96575aade624daa5a2f9fd6d83
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index 7380189..a7313c5 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -29,7 +29,7 @@
 osmo-build-dep.sh libosmo-sccp
 PARALLEL_MAKE="" osmo-build-dep.sh libsmpp34
 osmo-build-dep.sh openggsn
-osmo-build-dep.sh osmo-mgw pre_release # move to 'master' once the split is complete
+osmo-build-dep.sh osmo-mgw
 
 if [ "x$IU" = "x--enable-iu" ]; then
 	osmo-build-dep.sh libasn1c