Remove pre-C++11 code from std_placeholders.hpp

include/boost/bind/std_placeholders.hpp

@@ -11,12 +11,7 @@
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
-#include <boost/bind/detail/requires_cxx11.hpp>
 #include <boost/is_placeholder.hpp>
-#include <boost/config.hpp>
-
-#if !defined(BOOST_NO_CXX11_HDR_FUNCTIONAL) && !defined(BOOST_NO_CXX11_DECLTYPE) && !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
-
 #include <functional>
 #include <type_traits>
 
@@ -35,6 +30,4 @@ template<> struct is_placeholder< typename std::decay<decltype(std::placeholders
 
 } // namespace boost
 
-#endif
-
 #endif // #ifndef BOOST_BIND_STD_PLACEHOLDERS_HPP_INCLUDED