AK: Remove virtual destructors from non-virtual classes

Problem:
- Some classes have `virtual` destructors despite not having any
  virtual functions. This causes the classes to have a v-table and
  perform extra jumps at destruction time when there is no need.

Solution:
- Remove `virtual` keyword from destructors where there are no other
  virtual functions.
- Remove the destructor completely when the default destructor can be
  used.

AK/IntrusiveRedBlackTree.h

@@ -17,7 +17,7 @@ template<Integral K, typename V, IntrusiveRedBlackTreeNode<K> V::*member>
 class IntrusiveRedBlackTree : public BaseRedBlackTree<K> {
 public:
     IntrusiveRedBlackTree() = default;
-    virtual ~IntrusiveRedBlackTree() override
+    ~IntrusiveRedBlackTree()
     {
         clear();
     }