Libraries: Use default constructors/destructors in LibGUI

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/Libraries/LibGUI/Tray.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -21,10 +22,6 @@ Tray::Tray()
     set_focus_policy(GUI::FocusPolicy::TabFocus);
 }
 
-Tray::~Tray()
-{
-}
-
 Gfx::IntRect Tray::Item::rect(Tray const& tray) const
 {
     static constexpr int item_height = 22;