Remove static_assert workaround

include/boost/system/detail/std_category.hpp

@@ -51,12 +51,8 @@ public:
         // here when Id != 0, but this should never happen now because this code
         // path is no longer used
 
-#if !defined(BOOST_NO_CXX11_STATIC_ASSERT)
-
         static_assert( Id == 0, "This constructor should only be called with Id == 0 under MS STL 14.0+" );
 
-#endif
-
 #endif
     }