Please remove the unmaintained magithub.

It uses v2 of the Github api which has been disabled more than a year ago, see nex3/magithub#11 and https://github.com/blog/1160-github-api-v2-end-of-life. It also uses a symbol from Magit which no longer exists, resulting in that being repeatedly reported as a Magit bug, see nex3/magithub#12, magit/magit#789, and magit/magit#1003. Also the author, @nex3, does not reply to reports about these issues. There also is a pull request nex3/magithub#13 that supposedly fixes the first issue.