build: cleanup includes of <gmodule.h>

<gmodule.h> is implicitly included by <gio/gio.h> which is available
everywhere. For that reason, we would not have to include this header
at all. However, it is recommended to explicitly include <gmodule.h>
where needed.

So, include it where needed -- if <gio/gio.h> wouldn't be there --
and drop it from where it is not needed.

clients/common/nm-vpn-helpers.c

@@ -28,7 +28,6 @@
 #include "nm-vpn-helpers.h"
 
 #include <string.h>
-#include <gmodule.h>
 
 #include "nm-utils.h"
 

libnm-core/nm-vpn-editor-plugin.c

@@ -25,6 +25,7 @@
 #include "nm-vpn-editor-plugin.h"
 
 #include <dlfcn.h>
+#include <gmodule.h>
 
 #include "nm-core-internal.h"
 

src/main-utils.c

@@ -31,7 +31,6 @@
 
 #include <glib/gstdio.h>
 #include <glib-unix.h>
-#include <gmodule.h>
 
 #include "main-utils.h"
 #include "NetworkManagerUtils.h"

src/main.c

@@ -31,7 +31,6 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <gmodule.h>
 #include <string.h>
 #include <sys/resource.h>
 

src/settings/plugins/keyfile/plugin.c

@@ -26,7 +26,6 @@
 #include <sys/types.h>
 #include <string.h>
 
-#include <gmodule.h>
 #include <glib/gstdio.h>
 
 #include "nm-connection.h"