MarsSeed [1] filed a deletion request for libevent-fb [2]: Orphaned package, last updated in 2017.
Slightly modified version of [core] libevent, but the latter is much newer. This one still uses python2, though it is undeclared. No package specifically needs this variant. Safe to delete. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/libevent-fb/
