basic: include only what we use

This is a cleaned up result of running iwyu but without forward
declarations on src/basic.

src/basic/siphash24.c

@@ -18,9 +18,8 @@
 */
 
 #include "siphash24.h"
-#include "sparse-endian.h"
+#include "macro.h"
 #include "unaligned.h"
-#include "util.h"
 
 static inline uint64_t rotate_left(uint64_t x, uint8_t b) {
         assert(b < 64);