[includes] replace header guards with #pragma once

lib/tga/include/lib/tga.h

@@ -5,13 +5,10 @@
  * license that can be found in the LICENSE file or at
  * https://opensource.org/licenses/MIT
  */
-#ifndef __LIB_TGA_H
-#define __LIB_TGA_H
+#pragma once
 
 #include <lib/gfx.h>
 #include <sys/types.h>
 
 gfx_surface *tga_decode(const void *ptr, size_t len, gfx_format format);
 
-#endif
-