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/DragOperation.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -20,10 +21,6 @@ DragOperation::DragOperation(Core::Object* parent)
 {
 }
 
-DragOperation::~DragOperation()
-{
-}
-
 DragOperation::Outcome DragOperation::exec()
 {
     VERIFY(!s_current_drag_operation);