debian: prerm: remove obsolete code

this code has been obsoleted by commit 56607800, eb18af4c and 707be87a.

debian/qubes-core-agent.prerm

@@ -30,19 +30,6 @@ set -e
 # the debian-policy package
 
 if [ "$1" = "remove" ] ; then
-    # no more packages left
-    if [ -e /var/lib/qubes/fstab.orig ] ; then
-        mv /var/lib/qubes/fstab.orig /etc/fstab
-    fi
-
-    if [ -d /var/lib/qubes/removed-udev-scripts ] ; then
-        mv /var/lib/qubes/removed-udev-scripts/* /etc/udev/rules.d/
-    fi
-
-    if [ -e /var/lib/qubes/serial.orig ] ; then
-        mv /var/lib/qubes/serial.orig /etc/init/serial.conf
-    fi
-
     for init in plymouth-shutdown \
             prefdm \
             splash-manager \