I'm not sure what you have done. Removing the registration link is simply a matter of removing 'registration.php'(including the quotes and the comma) from the specified line. If you are seeing error messages, then you've done something wrong.
If you are unable to correct the problem, then get a fresh copy of the file, and replace the modified one.
We will guide you on what and where you can make changes, but if you wish us to make the changes for you, then we have to charge a fee for that. Free help you receive is not free for us.