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/FontPicker.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -169,10 +170,6 @@ FontPicker::FontPicker(Window* parent_window, const Gfx::Font* current_font, boo
     set_font(current_font);
 }
 
-FontPicker::~FontPicker()
-{
-}
-
 void FontPicker::set_font(const Gfx::Font* font)
 {
     if (m_font == font)