Libraries: Use default constructors/destructors in LibDesktop

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/LibDesktop/AppFile.cpp

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
  * Copyright (c) 2021, Spencer Dixon <spencercdixon@gmail.com>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -48,10 +49,6 @@ AppFile::AppFile(StringView path)
 {
 }
 
-AppFile::~AppFile()
-{
-}
-
 bool AppFile::validate() const
 {
     if (m_config->read_entry("App", "Name").trim_whitespace().is_empty())