Style: Replace header guards with #pragma once

scene/resources/external_texture.h

@@ -28,8 +28,7 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
 /**************************************************************************/
 
-#ifndef EXTERNAL_TEXTURE_H
-#define EXTERNAL_TEXTURE_H
+#pragma once
 
 #include "scene/resources/texture.h"
 
@@ -65,5 +64,3 @@ public:
 	ExternalTexture();
 	~ExternalTexture();
 };
-
-#endif // EXTERNAL_TEXTURE_H