Cleanup of systemd service files

Let's use a symlink in debian/ as we do in other projects,
and merge the two service files since anyway they call the same binary.

Change-Id: Ibd82ec12cbeb73a27ca5860266587efb58be14ab
diff --git a/contrib/osmo-pcu.service b/contrib/osmo-pcu.service
index 3066a66..6329d31 100644
--- a/contrib/osmo-pcu.service
+++ b/contrib/osmo-pcu.service
@@ -1,5 +1,5 @@
 [Unit]
-Description=sysmocom sysmoPCU
+Description=Osmocom osmo-pcu
 
 [Service]
 Type=simple
@@ -14,4 +14,3 @@
 
 [Install]
 WantedBy=multi-user.target
-Alias=sysmopcu.service