LibWeb: Remove broken spec link from MutationObserver

The link no longer works, and they are described as weak in the very
next comment as well.

Author: gmta

Libraries/LibWeb/DOM/MutationObserver.h

@@ -58,7 +58,6 @@ class MutationObserver final : public Bindings::PlatformObject {
     GC::Ptr<WebIDL::CallbackType> m_callback;
 
     // https://dom.spec.whatwg.org/#mutationobserver-node-list
-    // NOTE: These are weak, per https://dom.spec.whatwg.org/#garbage-collection
     // Registered observers in a node’s registered observer list have a weak reference to the node.
     Vector<GC::Weak<Node>> m_node_list;