Remove MailPoet CSS files

code-snippet.php

<?php
// Force removal of styles
add_filter('print_styles_array', 'custom_print_styles_array');
/**
 * Force removal of styles that are not enqued properly
 */
function custom_print_styles_array($styles){
	$styles_to_remove = array(	
		'mailpoet_public',				// plugins/mailpoet
		'mailpoet_custom_fonts_css' 	// plugins/mailpoet
	);

	if(is_array($styles) && count($styles) > 0){
		foreach($styles as $key => $code){
			if(in_array($code, $styles_to_remove)){
				unset($styles[$key]);
			}
		}
	}

	return $styles;
}

/**
 * Source: https://wordpress.org/support/topic/remove-stylesheet-3/
 */