Refactor redirects code

[humitos]

After merging #6398 there are some Python logic code that can be almost completely deleted (redirects.models.Redirect.redirect_* methods).

Besides, as Eric mentioned we can also remove the dependency of passing some attributes to redirects.querysets.RedirectQuerySetBase.get_redirect_path_with_status

[humitos]

@ericholscher I took a look at this today.

I'm not sure we can remove the lang_slug and version_slug from that method. It's used for resolve_path to get the full path to redirect to.

On the other hand, my idea of removing the redirect_* method may not be possible either. There are some Python logic there (like re.sub to remove a part of the URL) that I don't think we can easily move into the DB or if it does make sense. I think we can only remove some if checks, but not too much more than that.

Let me know if there are something that I'm not seeing here.