remove sys/sysctl.h

this functionality has essentially always been deprecated in linux,
and was never supported by musl. the presence of the header was
reported to cause some software to attempt to use the nonexistant
function, so removing the header is the cleanest solution.

include/sys/sysctl.h

@@ -1,17 +0,0 @@
-#ifndef	_SYS_SYSCTL_H
-#define	_SYS_SYSCTL_H
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-#define __NEED_size_t
-#include <bits/alltypes.h>
-
-int sysctl (int *, int, void *, size_t *, void *, size_t);
-
-#ifdef __cplusplus
-}
-#endif
-
-#endif