Fix Windows exports for header members

Author: sentientsergio

include/boost/http_proto/detail/header.hpp

@@ -157,20 +157,16 @@ struct BOOST_HTTP_PROTO_DECL header
     static header&
     get(fields_base& f) noexcept;
 
-    BOOST_HTTP_PROTO_DECL
     static header const*
     get_default(detail::kind k) noexcept;
 
     // called from parser
     explicit header(empty) noexcept;
 
-    BOOST_HTTP_PROTO_DECL
     header(detail::kind) noexcept;
 
-    BOOST_HTTP_PROTO_DECL
     void swap(header&) noexcept;
 
-    BOOST_HTTP_PROTO_DECL
     bool keep_alive() const noexcept;
 
     static std::size_t bytes_needed(

include/boost/http_proto/header_limits.hpp

@@ -116,7 +116,6 @@ struct header_limits
         number of contiguous bytes of storage
         that would be needed at these settings.
     */
-    BOOST_HTTP_PROTO_DECL
     std::size_t
     valid_space_needed() const;
 };