[arch-dev-public] Disable corepkg?

Hi, Since we don't want people to push to core directly how about removing corepkg from devtools? For the few cases where pushing to core directly is needed one can simply use "commitpkg core" instead. If nobody objects I'll submit a patch to devtools in about a week. Tracking bug so I don't forget: https://bugs.archlinux.org/task/41013