TT#124273 use symlinks instead of Install/Alias for aliases

The aliases created by systemd under Install/Alias are created and
removed as the service is enabled and disabled, and don't serve as
generic alias names. Furthermore they seem to linger behind when the
package is removed or replaced, which leads to collisions and
installation failures when the NGCP-specific package is replaced by the
non-NGCP version.

Change-Id: I2313ffffb1fa4fb1d570b23113b0618744c58e26

debian/ngcp-rtpengine-daemon.links

@@ -0,0 +1,2 @@
+/lib/systemd/system/ngcp-rtpengine-daemon.service	/lib/systemd/system/rtpengine-daemon.service
+/lib/systemd/system/ngcp-rtpengine-daemon.service	/lib/systemd/system/rtpengine.service

debian/ngcp-rtpengine-daemon.service

@@ -14,4 +14,3 @@ ExecStopPost=/usr/sbin/ngcp-rtpengine-iptables-setup stop
 
 [Install]
 WantedBy=multi-user.target
-Alias=rtpengine.service

debian/ngcp-rtpengine-recording-daemon.links

@@ -0,0 +1,2 @@
+/lib/systemd/system/ngcp-rtpengine-recording-daemon.service	/lib/systemd/system/rtpengine-recording-daemon.service
+/lib/systemd/system/ngcp-rtpengine-recording-daemon.service	/lib/systemd/system/rtpengine-recording.service

debian/ngcp-rtpengine-recording-daemon.service

@@ -14,4 +14,3 @@ ExecStart=/usr/sbin/rtpengine-recording -f -E --no-log-timestamps --pidfile /run
 
 [Install]
 WantedBy=multi-user.target
-Alias=rtpengine-recording.service