magit-log-edit-commit: use magit-run-git-with-input for commits too

In `magit-log-edit-commit' use `magit-run-git-with-input' instead of
`magit-run-git-async-with-input' when editing commit messages, not only
when editing tag messages.

The latter was removed from `magit.el' some time ago but instead defined
here.  But now `magit-run-git*' which it uses has also been removed from
`magit.el'.