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/Set.cpp

@@ -19,10 +19,6 @@ Set::Set(Object& prototype)
 {
 }
 
-Set::~Set()
-{
-}
-
 void Set::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);