removed unused function

lib/single-file/doc-helper.js

@@ -387,15 +387,6 @@ this.docHelper = this.docHelper || (() => {
 		return docTypeString + doc.documentElement.outerHTML;
 	}
 
-	function getFontKey(style) {
-		return JSON.stringify([
-			style.fontFamily,
-			style.fontWeight,
-			style.fontStyle,
-			style.fontVariant
-		]);
-	}
-
 	function removeQuotes(string) {
 		if (string.match(REGEXP_SIMPLE_QUOTES_STRING)) {
 			string = string.replace(REGEXP_SIMPLE_QUOTES_STRING, "$1");