remove unused code from md plugin

plugin/markdown/markdown.js

@@ -408,16 +408,6 @@ const Plugin = () => {
 
 			deck = reveal;
 
-			// This should no longer be needed, as long as the highlight.js
-			// plugin is included after the markdown plugin
-			// if( typeof window.hljs !== 'undefined' ) {
-			// 	marked.setOptions({
-			// 		highlight: function( code, lang ) {
-			// 			return window.hljs.highlightAuto( code, lang ? [lang] : null ).value;
-			// 		}
-			// 	});
-			// }
-
 			// marked can be configured via reveal.js config options
 			var options = deck.getConfig().markdown;
 			if( options ) {