Uninstall xmltex
To remove just xmltex package itself from Debian Unstable (Sid) execute on terminal:
sudo apt-get remove xmltex
Uninstall xmltex and it's dependent packages
To remove the xmltex package and any other dependant package which are no longer needed from Debian Sid.
sudo apt-get remove --auto-remove xmltex
Purging xmltex
If you also want to delete configuration and/or data files of xmltex from Debian Sid then this will work:
sudo apt-get purge xmltex
To delete configuration and/or data files of xmltex and it's dependencies from Debian Sid then execute:
sudo apt-get purge --auto-remove xmltex
See Also
How to remove xmltex package from Debian Unstable (Sid)