Prune elements with display none to fix regression.

In an earlier emogridier version (til WC 3.9.3) this was happening by
default, however now we have to do this explicitly since we update
emogrifier to > 3.x.

includes/emails/class-wc-email.php

@@ -567,6 +567,9 @@ class WC_Email extends WC_Settings_API {
 					do_action( 'woocommerce_emogrifier', $emogrifier, $this );
 
 					$content    = $emogrifier->emogrify();
+					$html_prune = \Pelago\Emogrifier\HtmlProcessor\HtmlPruner::fromHtml( $content );
+					$html_prune->removeElementsWithDisplayNone();
+					$content    = $html_prune->render();
 				} catch ( Exception $e ) {
 					$logger = wc_get_logger();
 					$logger->error( $e->getMessage(), array( 'source' => 'emogrifier' ) );