postrm is in libglobus-authz-callout-error-doc 3.6-1.
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 | #!/bin/sh
set -e
dpkg-maintscript-helper symlink_to_dir \
    /usr/share/doc/libglobus-authz-callout-error-doc \
    libglobus-authz-callout-error-dev 3.5-2~ \
    libglobus-authz-callout-error-doc -- "$@"
 |