Userland/Applets: 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/Applets/Keymap/KeymapStatusWindow.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Timur Sultanov <SultanovTS@yandex.ru>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -30,10 +31,6 @@ KeymapStatusWindow::KeymapStatusWindow()
     m_status_widget->set_text(current_keymap_name.substring(0, 2));
 }
 
-KeymapStatusWindow::~KeymapStatusWindow()
-{
-}
-
 void KeymapStatusWindow::wm_event(GUI::WMEvent& event)
 {
     if (event.type() == GUI::WMEvent::WM_KeymapChanged) {