How do I remove Google Fonts from a parent theme?

You may also want to try to deregister the style within your function since it has been register in the parent theme function.

Try:

function remove_google_fonts_stylesheet() {
     wp_dequeue_style( 'pixgraphy_google_fonts' );
     wp_deregister_style('pixgraphy_google_fonts');
}
add_action( 'wp_enqueue_scripts', 'remove_google_fonts_stylesheet', 100 );