backend-headless: fix comment on use_pixman

The default is no-op, not GL. It doesn't even support GL.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

include/libweston/backend-headless.h

@@ -39,7 +39,7 @@ extern "C" {
 struct weston_headless_backend_config {
 	struct weston_backend_config base;
 
-	/** Whether to use the pixman renderer instead of the OpenGL ES renderer. */
+	/** Whether to use the pixman renderer, default is no-op */
 	bool use_pixman;
 };