How to avoid conflict with Contact Form 7 and Formidable

I just discovered that contact form 7 was stopping my formidable registration form from working with this error popping up.

Fatal error: Call to undefined method PHPMailer::getCustomHeaders() in wp-contentpluginscontact-form-7includesmail.php on line 176

So what you can do is add the following code to your functions.php file in your child theme directory.

// Deregister Contact Form 7 JavaScript files on all pages without a form
add_action( 'wp_enqueue_scripts', 'aa_deregister_javascript', 100 );
function aa_deregister_javascript() {
    if ( ! is_page( array( 1904, 1906, 1909) ) ) {
        wp_deregister_script( 'contact-form-7' );
    }
}

Replace the numbers, ie 1904, with the page or post numbers that have the Contact Form 7 form on them.
If you have a Contact Form 7 form on every page of the website, ie in the footer, consider changing it to a formidable form.

This also has the added benefit of speeding up pages that don't require Contact Form 7!