vendor: roll back golang.org/x/sys to fix compile

Until https://github.com/golang/go/issues/21136 is fixed

vendor/golang.org/x/sys/unix/mkerrors.sh

@@ -75,7 +75,6 @@ includes_DragonFly='
 '
 
 includes_FreeBSD='
-#include <sys/capability.h>
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/event.h>
@@ -402,7 +401,6 @@ ccflags="$@"
 		$2 ~ /^(BPF|DLT)_/ ||
 		$2 ~ /^CLOCK_/ ||
 		$2 ~ /^CAN_/ ||
-		$2 ~ /^CAP_/ ||
 		$2 ~ /^ALG_/ ||
 		$2 ~ /^FS_(POLICY_FLAGS|KEY_DESC|ENCRYPTION_MODE|[A-Z0-9_]+_KEY_SIZE|IOC_(GET|SET)_ENCRYPTION)/ ||
 		$2 ~ /^GRND_/ ||