Remove the wesconfig.h dependency from config.hpp.

The dependency is not needed and causes a lot of files to be compiled
when Wesnoth's version number changes.

src/config.hpp

@@ -40,7 +40,6 @@
 
 #include "game_errors.hpp"
 #include "tstring.hpp"
-#include "wesconfig.h"
 
 class config;
 struct tconfig_implementation;

src/game.cpp

@@ -38,6 +38,7 @@
 #include "serialization/validator.hpp"
 #include "statistics.hpp"
 #include "version.hpp"
+#include "wesconfig.h"
 #include "wml_exception.hpp"
 
 #include <cerrno>