prerm is in caca-utils 0.99.beta18-1ubuntu5.
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 | #!/bin/sh
set -e
if [ "$1" = remove ]; then
  # Remove old alternative for figlet
  update-alternatives --remove figlet /usr/bin/toilet
fi
 |