Contact Form 7 plugin: Clean up global scripts & styles.

contactform7.php

<?php

add_action( 'wp_enqueue_scripts', 'ddw_cf7_cleanup' );
/**
 * Contact Form 7 plugin: Cleanup global scripts & styles.
 *
 * @author David Decker - DECKERWEB
 * @link   http://deckerweb.de/twitter
 */
function ddw_cf7_cleanup() {

	/** Dequeue globally enqueued scripts & styles */
	wp_dequeue_script( 'contact-form-7' );
	wp_dequeue_style( 'contact-form-7' );

	/** Only enqueue stuff on the used page ID */
	if ( is_page( '12' ) ) {

		wp_enqueue_script( 'contact-form-7' );
		wp_enqueue_style( 'contact-form-7' );

	}  // end if

}  // end function

Above code will load only on specific page/post. Instead, use below code to load CF7 JS and CSS when content contains CF7 shortcodes. It will work with any post type.
https://gist.github.com/cyberwani/38f945007e83600ca0bf0bc48d99361b