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/gstlibcameraallocator.h

@@ -6,8 +6,7 @@
  * gstlibcameraallocator.h - GStreamer Custom Allocator
  */
 
-#ifndef __GST_LIBCAMERA_ALLOCATOR_H__
-#define __GST_LIBCAMERA_ALLOCATOR_H__
+#pragma once
 
 #include <gst/gst.h>
 #include <gst/allocators/allocators.h>
@@ -30,5 +29,3 @@ gsize gst_libcamera_allocator_get_pool_size(GstLibcameraAllocator *allocator,
 					    libcamera::Stream *stream);
 
 libcamera::FrameBuffer *gst_libcamera_memory_get_frame_buffer(GstMemory *mem);
-
-#endif /* __GST_LIBCAMERA_ALLOCATOR_H__ */