[PRQ#43585] Deletion Request for trac-mercurial

MarsSeed [1] filed a deletion request for trac-mercurial [2]: Unneeded python2 based addon for trac. The latter is broken since Nov 2021 and is now submitted for deletion (PRQ#43579). Safe to delete this abandoned, unused package as well. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/trac-mercurial/