cleanup: Switch to pragma once

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3157>

src/backends/native/meta-kms-utils.h

@@ -17,8 +17,7 @@
  * 02111-1307, USA.
  */
 
-#ifndef META_KMS_UTILS_H
-#define META_KMS_UTILS_H
+#pragma once
 
 #include <stddef.h>
 #include <stdint.h>
@@ -39,5 +38,3 @@ int64_t meta_calculate_drm_mode_vblank_duration_us (const drmModeModeInfo *drm_m
 
 const char * meta_drm_format_to_string (MetaDrmFormatBuf *tmp,
                                         uint32_t          drm_format);
-
-#endif /* META_KMS_UTILS_H */