remove BOOST_STATIC_ASSERT fallback

Author: grisumbras

include/boost/json/detail/config.hpp

@@ -12,6 +12,7 @@
 
 #include <boost/config.hpp>
 #include <boost/assert.hpp>
+#include <boost/static_assert.hpp>
 #include <boost/throw_exception.hpp>
 #include <cstdint>
 #include <type_traits>
@@ -47,10 +48,6 @@
 # endif
 #endif
 
-#ifndef BOOST_STATIC_ASSERT
-#define BOOST_STATIC_ASSERT( ... ) static_assert(__VA_ARGS__, #__VA_ARGS__)
-#endif
-
 #ifndef BOOST_FALLTHROUGH
 #define BOOST_FALLTHROUGH [[fallthrough]]
 #endif