Remove the superfluous `PDFJS.disableFontFace = false;` statement at the top of font_loader.js (issue 6742)

Fixes 6742.

src/display/font_loader.js

@@ -17,8 +17,6 @@
 
 'use strict';
 
-PDFJS.disableFontFace = false;
-
 function FontLoader(docId) {
   this.docId = docId;
   this.styleElement = null;