Scimmia [1] filed a deletion request for calibre-beta [2]: Package in Community has been updated to the beta version, so this is no longer useful. Betas are very rare for Calibre, so this won't be useful in the future, either.
[1] https://aur.archlinux.org/account/Scimmia/ [2] https://aur.archlinux.org/pkgbase/calibre-beta/
