fixed cssTree issue

lib/single-file/modules/css-fonts-alt-minifier.js

@@ -235,7 +235,6 @@ this.fontsAltMinifier = this.fontsAltMinifier || (() => {
 	}
 
 	function getPropertyValue(ruleData, propertyName) {
-		const cssTree = this.fontsAltMinifier.cssTree;
 		let property;
 		if (ruleData.block.children) {
 			property = ruleData.block.children.filter(node => node.property == propertyName).tail;