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/Date.cpp

@@ -28,10 +28,6 @@ Date::Date(double date_value, Object& prototype)
 {
 }
 
-Date::~Date()
-{
-}
-
 String Date::iso_date_string() const
 {
     int year = year_from_time(m_date_value);