fontforge: remove obsolete comment
This was added in 07d12fbef1c ("fontforge: get rid of output hash
depending on git"), to explain the line:
export GIT="$(type -P true)".
This line was removed in e9848d11ad0 ("fontforge: 20190801 -> 20200314"),
but I forgot to remove the comment.
Fixes: e9848d11ad0 ("fontforge: 20190801 -> 20200314")