Forbid b{copy,zero,cmp}(). Don't include <strings.h> for <string.h>

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12996

module/os/freebsd/zfs/crypto_os.c

@@ -39,8 +39,6 @@ __FBSDID("$FreeBSD$");
 #include <sys/sysctl.h>
 #include <opencrypto/cryptodev.h>
 #include <opencrypto/xform.h>
-#else
-#include <strings.h>
 #endif
 
 #include <sys/zio_crypt.h>