gstreamer: Convert to pragma once

Remove the verbose #ifndef/#define/#endif pattern for maintaining
header idempotency, and replace it with a simple #pragma once.

This simplifies the headers, and prevents redundant changes when
header files get moved.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>

src/gstreamer/gstlibcamera-utils.h

@@ -6,8 +6,7 @@
  * gstlibcamera-utils.h - GStreamer libcamera Utility Functions
  */
 
-#ifndef __GST_LIBCAMERA_UTILS_H__
-#define __GST_LIBCAMERA_UTILS_H__
+#pragma once
 
 #include <libcamera/camera_manager.h>
 #include <libcamera/stream.h>
@@ -71,5 +70,3 @@ public:
 private:
 	GRecMutex *mutex_;
 };
-
-#endif /* __GST_LIBCAMERA_UTILS_H__ */