LibWeb: Delete public constructor of FontFaceSet

The IDL definition in the spec does not have a public constructor, and
our test that relies on it was failing to run in other browsers.

Tests/LibWeb/Text/input/css/FontFaceSet-setlike.html

@@ -2,7 +2,7 @@
 <script src="../include.js"></script>
 <script>
     test(() => {
-        const fontFaceSet = new FontFaceSet([]);
+        const fontFaceSet = document.fonts;
         const fontFace = new FontFace("Hash Sans", 'url(../../../../Ref/assets/HashSans.woff)');
 
         println("-- Empty FontFaceSet --");

Userland/Libraries/LibWeb/CSS/FontFaceSet.idl

@@ -17,8 +17,6 @@ enum FontFaceSetLoadStatus { "loading", "loaded" };
 // https://drafts.csswg.org/css-font-loading/#fontfaceset
 [Exposed=(Window,Worker)]
 interface FontFaceSet : EventTarget {
-    constructor(sequence<FontFace> initialFaces);
-
     setlike<FontFace>;
     FontFaceSet add(FontFace font);
     boolean delete(FontFace font);