xxd is no longer a dependency of vim-common, quotings vim's Debian
package changelog (also see
https://metadata.ftp-master.debian.org/changelogs/main/v/vim/unstable_changelog):
| vim (2:9.0.0135-1) unstable; urgency=medium
|
| [...]
| * Remove "Depends: xxd" from vim-common (Closes: #1007887)
Since we always shipped xxd with grml-small and grml-full, let's
make sure we continue to provide it.