Applications: Use default constructors/destructors

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/Applications/Spreadsheet/Spreadsheet.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2021, the SerenityOS developers.
+ * Copyright (c) 2020-2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -81,10 +81,6 @@ Sheet::Sheet(Workbook& workbook)
     }
 }
 
-Sheet::~Sheet()
-{
-}
-
 JS::Interpreter& Sheet::interpreter() const
 {
     return const_cast<JS::Interpreter&>(*m_interpreter);