Change headers slightly.

Author: mjp41

src/snmalloc/ds_core/seqset.h

@@ -1,7 +1,7 @@
 #pragma once
 
 #include "../aal/aal.h"
-#include "../ds_core/ds_core.h"
+#include "defines.h"
 #include "snmalloc/stl/type_traits.h"
 #include "snmalloc/stl/utility.h"