Remove outdated advice for magit-visit

magit-visit was removed a while ago [1], so this isn't doing anything.
Currently, there are multiple functions to advise [2]. Instead of doing
that, I'll just call org-reveal (C-c C-r).

[1] 81c6b881d9e4e93442677d6e2183c7f2cc47887a
[2] 2dc3965e74eabe53763f208809a9dae3105c1149
Update for git-commit-mode rename