Ensure https enforcement for login/acct creation only happens on mobile

Without this change, if wgMFForceSecureLogin is set to true, then all
attempts to access account creation will be sent to the mobile version
of the site, even if the request was made from the desktop version of
the site. This was a bone-headed oversight.

Change-Id: If8cb2e7d81c8466b1506bde19ffd4a4ab061d2b0
Merge "Ensure https enforcement for login/acct creation only happens on mobile"