LibHTML: Oops, fix build.

It's another "hacking on the train and forgetting to try a full build"
episode, this time starring LibHTML.

Libraries/LibHTML/Frame.cpp

@@ -69,14 +69,14 @@ RefPtr<LayoutNode> Frame::generate_layout_tree(const StyledNode& styled_root)
         }
     };
 
-    Function<RefPtr<LayoutNode>(const StyledNode&, LayoutNode*)> build_layout_tree;
-    build_layout_tree = [&](const StyledNode& styled_node, LayoutNode* parent_layout_node) -> RefPtr<LayoutNode> {
+    Function<RefPtr<LayoutNode>(const StyledNode&)> build_layout_tree;
+    build_layout_tree = [&](const StyledNode& styled_node) -> RefPtr<LayoutNode> {
         auto layout_node = create_layout_node(styled_node);
         if (!layout_node)
             return nullptr;
         if (styled_node.has_children()) {
             for (auto* styled_child = styled_node.first_child(); styled_child; styled_child = styled_child->next_sibling()) {
-                auto layout_child = build_layout_tree(*styled_child, layout_node.ptr());
+                auto layout_child = build_layout_tree(*styled_child);
                 if (!layout_child)
                     continue;
                 layout_node->append_child(*layout_child);
@@ -85,7 +85,7 @@ RefPtr<LayoutNode> Frame::generate_layout_tree(const StyledNode& styled_root)
         return layout_node;
     };
 
-    return build_layout_tree(styled_root, nullptr);
+    return build_layout_tree(styled_root);
 }
 
 void Frame::layout()