TT#32220 Cleanup related with permanent use of "policy-rc.d" and migration to systemd

For a long time our installation and upgrade uses a temporary "policy-rc.d" to
prevent to [re]start services in the middle of the installation, so some uses of
"invoke-rc.d" (which defers to "policy-rc.d") can cause changes in behaviour.

Upon review because of this change, we found out that the restart of kamailio
when updating ngcp-db-schema didn't happen for a long time because of the use of
"policy-rc.d" that we were using during installations of upgrades in the last
few months/years, but besides this, the code is obsolete since quite a while
ago.

So we drop it completely now.

Change-Id: I76eae2fbda340a1021f10d28f95e76b35ea92c90

debian/ngcp-db-schema.postinst

@@ -1,36 +0,0 @@
-#!/bin/sh
-
-set -e
-
-case "$1" in
-    configure)
-        # apply bugfix on 2.6 ngcp systems with broken db rev script
-        # /usr/share/ngcp-db-schema/db_scripts/diff/9868.up
-        # ngcp 2.5 repos provides ngcp-db-schema := 0.1.3
-        # ngcp 2.6 repos provides ngcp-db-schema >= 2.6.3
-        if [ -n "$2" ] && dpkg --compare-versions "$2" ge 2.6.0 && dpkg --compare-versions "$2" le 2.6.4 ; then
-            echo  "Executing ngcp-update-db-schema to address 2.6 db rev script bug."
-            ngcp-update-db-schema
-
-            if /etc/init.d/kamailio-proxy status >/dev/null ; then
-               if [ -x "$(which invoke-rc.d 2>/dev/null)" ]; then
-		   echo  "Restarting kamailio proxy to handle db changes"
-                   invoke-rc.d kamailio-proxy restart || exit $?
-               else
-		   echo  "Restarting kamailio proxy to handle db changes"
-                   /etc/init.d/kamailio-proxy restart || exit $?
-               fi
-            fi
-        fi
-    ;;
-
-    abort-upgrade|abort-remove|abort-deconfigure)
-    ;;
-
-    *)
-        echo "postinst of ngcp-db-schema called with unknown argument \`$1'" >&2
-        exit 1
-    ;;
-esac
-
-exit 0