Some mixed up comments in registration templates

[medihack]

Some minor issue, but the comments in registration/admin_approve_complete.html, registration/admin_approve_complete_email.txt and registration/admin_approve_complete_email.html are a bit mixed up.

The comment section at the bottom of registration/admin_approve_complete.html belongs to admin_approve_complete_email.html and admin_approve_complete_email.txt, and vice versa.