Move modules.h to core/maxscale

Also remove some unnecessary includes + cleanup

server/core/load_utils.c

@@ -34,7 +34,6 @@
 #include <unistd.h>
 #include <string.h>
 #include <dlfcn.h>
-#include <maxscale/modules.h>
 #include <maxscale/modinfo.h>
 #include <maxscale/log_manager.h>
 #include <maxscale/version.h>
@@ -45,6 +44,8 @@
 #include <maxscale/gwdirs.h>
 #include <maxscale/alloc.h>
 
+#include "maxscale/modules.h"
+
 typedef struct loaded_module
 {
     char    *module;       /**< The name of the module */