LibWeb: Implement Element.removeAttributeNode()

Author: https://github.com/awesomekling
Commit: 20bdda7f02
Pull-request: https://github.com/SerenityOS/serenity/pull/23964

Tests/LibWeb/Text/input/DOM/Element-removeAttributeNode.html

@@ -0,0 +1,16 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        let e = document.createElement("div");
+        e.setAttribute("foo", "bar");
+        let a = e.getAttributeNode("foo");
+        let removed = e.removeAttributeNode(a);
+        println(a === removed);
+        try {
+            e.removeAttributeNode(a);
+            println("FAIL");
+        } catch (e) {
+            println("OK: " + e);
+        }
+    });
+</script>