test: 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>

test/v4l2_subdevice/v4l2_subdevice_test.h

@@ -5,8 +5,7 @@
  * v4l2_subdevice_test.h - VIMC-based V4L2 subdevice test
  */
 
-#ifndef __LIBCAMERA_V4L2_SUBDEVICE_TEST_H__
-#define __LIBCAMERA_V4L2_SUBDEVICE_TEST_H__
+#pragma once
 
 #include <libcamera/framebuffer.h>
 
@@ -32,5 +31,3 @@ protected:
 	std::shared_ptr<libcamera::MediaDevice> media_;
 	libcamera::V4L2Subdevice *scaler_;
 };
-
-#endif /* __LIBCAMERA_V4L2_SUBDEVICE_TEST_H__ */