prerm is in git-el 1:2.1.4-2.1+deb8u6.
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 | #!/bin/sh
set -e
/usr/lib/emacsen-common/emacs-package-remove git
|