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/Event.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -19,10 +20,6 @@ DropEvent::DropEvent(const Gfx::IntPoint& position, const String& text, NonnullR
 {
 }
 
-DropEvent::~DropEvent()
-{
-}
-
 String KeyEvent::to_string() const
 {
     Vector<String, 8> parts;
@@ -56,8 +53,4 @@ ActionEvent::ActionEvent(Type type, Action& action)
 {
 }
 
-ActionEvent::~ActionEvent()
-{
-}
-
 }