How to stop PHP code running when in a child theme

Question

I understand you can add extra CSS on top of the parent theme, but how do you remove PHP code from functions.php?

I want to remove the Masonry plugin in twentyfourteen theme, and have located the piece of code on line 254.

    if ( is_active_sidebar( 'sidebar-3' ) ) {
    wp_enqueue_script( 'jquery-masonry' );
    }

If I'm editing the parent theme, I can just comment this block out /* */.

But I'm not aware of a way to change this is my child theme.