Style: Replace header guards with #pragma once

drivers/metal/metal_utils.h

@@ -28,8 +28,7 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
 /**************************************************************************/
 
-#ifndef METAL_UTILS_H
-#define METAL_UTILS_H
+#pragma once
 
 #import <os/log.h>
 
@@ -101,5 +100,3 @@ private:
 extern os_log_t LOG_DRIVER;
 // Used for dynamic tracing.
 extern os_log_t LOG_INTERVALS;
-
-#endif // METAL_UTILS_H