The users_Registration_Simple.php file is provided to give you an easy way to provide registration without Captcha.
However, you can remove the necessary form elements and spry validation from the users_Registration.php page instead. A How To is in the works to show you how to accomplish this, but here are a few pointers...
1. Remove all form elements for the Captcha image, and security question text field. (Lines 820 - 842 of an untouched users_Registration.php page)
2. Remove the Spry validation reference from the bottom of the file (Line 858). This line looks like this: