Services: Use default constructors/destructors

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#cother-other-default-operation-rules

"The compiler is more likely to get the default semantics right and
you cannot implement these functions better than the compiler."

Userland/Services/Taskbar/ShutdownDialog.h

@@ -17,7 +17,7 @@ public:
 
 private:
     ShutdownDialog();
-    virtual ~ShutdownDialog() override;
+    virtual ~ShutdownDialog() override = default;
 
     int m_selected_option { -1 };
 };