nir: Don't include bitscan.h in nir.h, it's not actually used.

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33439>

src/compiler/nir/nir.h

@@ -33,7 +33,6 @@
 #include "compiler/glsl/list.h"
 #include "compiler/shader_enums.h"
 #include "compiler/shader_info.h"
-#include "util/bitscan.h"
 #include "util/bitset.h"
 #include "util/compiler.h"
 #include "util/enum_operators.h"