Remove unnecessary SConfig from readwritesplit

The configuration doesn't need to be contained in shared pointer as each
session holds its own version of it. This removes most of the overhead in
configuration reloading. The only thing that's left is any overhead added
by the use of thread-local storage.

server/modules/routing/readwritesplit/rwsplit_mysql.cc

@@ -116,7 +116,7 @@ bool RWSplitSession::handle_target_is_all(route_target_t route_target, GWBUF *qu
     {
         // TODO: Append to the already stored session command instead of disabling history
         MXS_INFO("Large session write, have to disable session command history");
-        m_config->disable_sescmd_history = true;
+        m_config.disable_sescmd_history = true;
 
         continue_large_session_write(querybuf, qtype);
         result = true;