backend-drm: drop gbm.h from c files

The header file is anyway included in drm-internal.h, we can safely
drop it from the c files.

Signed-off-by: Stefan Agner <stefan@agner.ch>

libweston/backend-drm/drm.c

@@ -47,7 +47,6 @@
 #include <xf86drmMode.h>
 #include <drm_fourcc.h>
 
-#include <gbm.h>
 #include <libudev.h>
 
 #include <libweston/libweston.h>

libweston/backend-drm/fb.c

@@ -35,8 +35,6 @@
 #include <xf86drmMode.h>
 #include <drm_fourcc.h>
 
-#include <gbm.h>
-
 #include <libweston/libweston.h>
 #include <libweston/backend-drm.h>
 #include <libweston/pixel-formats.h>

libweston/backend-drm/kms.c

@@ -35,8 +35,6 @@
 #include <xf86drmMode.h>
 #include <drm_fourcc.h>
 
-#include <gbm.h>
-
 #include <libweston/libweston.h>
 #include <libweston/backend-drm.h>
 #include "shared/helpers.h"