prerm is in leafpad 0.8.18.1-4.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 | #!/bin/sh
set -e
case "$1" in
  remove|upgrade|deconfigure)
    # Unregister leafpad as a gnome-text-editor in the alternatives system.
    update-alternatives --remove gnome-text-editor /usr/bin/leafpad || :
    ;;
esac
 |