This reverts commit 3a2276b5.

Use http or https, depending on the value of `is_secure`.
This is similar to how links in some other email templates work.

To following the link in the password reset email

We used to use Django templates and the Sites framework. At some point we
stopped, but this was leftover. The site_name no longer gets set properly.
It's probably a config issue, but not one I want to deal with right before
release, so I'm hardcoding it to link to the prod edx.org site until we
 can sort what's what in the morning.