goodgerster [1] filed a deletion request for gimp-webp-bzr [2]: Project no longer uses bzr (moved to GitHub in 2015) and was merged into GIMP at least two years ago.
[1] https://aur.archlinux.org/account/goodgerster/ [2] https://aur.archlinux.org/pkgbase/gimp-webp-bzr/
