Provide postrm script

From: Michael Prokop <mprokop@sipwise.com>

debian/ngcp-mediator.postrm

@@ -0,0 +1,18 @@
+#!/bin/sh
+# postrm script for ngcp-mediator
+
+set -e
+
+removal_wrapper() {
+  # remove the init script only on ce systems, as the
+  # the pro system handle it inside the monitoring/HA setup
+  if ! [ -x "$(which ngcp-check_active 2>/dev/null)" ]; then
+    update-rc.d mediator remove >/dev/null
+  fi
+}
+
+if [ "$1" = "purge" ] ; then
+  removal_wrapper
+fi
+
+exit 0