Remove queued HTTP handler registration

websocketpp's socket handlers run at ultra-high priority which means they can beat registration of HTTP endpoints because they are queued via low priority.

No real reason needed to queue up registration of handlers at this point so just remove this queue

plugins/http_plugin/http_plugin.cpp

@@ -560,9 +560,7 @@ namespace eosio {
 
    void http_plugin::add_handler(const string& url, const url_handler& handler) {
       ilog( "add api url: ${c}", ("c",url) );
-      app().post(priority::low, [=](){
-        my->url_handlers.insert(std::make_pair(url,handler));
-      });
+      my->url_handlers.insert(std::make_pair(url,handler));
    }
 
    void http_plugin::handle_exception( const char *api_name, const char *call_name, const string& body, url_response_callback cb ) {