kern: devirtualize several KAutoObject functions

libraries/libmesosphere/include/mesosphere/kern_k_client_session.hpp

@@ -36,7 +36,6 @@ namespace ams::kern {
             }
 
             virtual void Destroy() override;
-            static void PostDestroy(uintptr_t arg) { MESOSPHERE_UNUSED(arg); /* ... */ }
 
             constexpr KSession *GetParent() const { return m_parent; }