Libraries: Use default constructors/destructors in LibJS

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/LibJS/Runtime/GeneratorObject.cpp

@@ -43,10 +43,6 @@ void GeneratorObject::initialize(GlobalObject&)
 {
 }
 
-GeneratorObject::~GeneratorObject()
-{
-}
-
 void GeneratorObject::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);