postrm is in gnus 5.11+v0.10.dfsg-3.
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 12 13 14 15 16 17 18 19 20 21 22 23 24 | #!/bin/sh
set -e
case "$1" in
  remove)
    rm -rf /usr/share/emacs/site-lisp/gnus
    ;;
  purge)
    rm -rf /usr/share/emacs/site-lisp/gnus
    for flavour in emacs20 emacs21 emacs22 xemacs20 xemacs21; do
	STARTFILE="/etc/${flavour}/site-start.d/20gnus-init.el";
        # we mimic dpkg as closely as possible, so we remove
        # configuration files with dpkg backup extensions too:
        for ext in '~' '%' .bak .ucf-new .ucf-old .ucf-dist; do
            rm -f $STARTDIR/20$STARTFILE$ext
        done
	rm -f ${STARTFILE}
	if [ -x /usr/bin/ucf ]; then
	    ucf --purge ${STARTFILE}
	fi
    done
    ;;
esac
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