commit bd648e3 ("mdadm: Remove klibc and uclibc support") removes
macro HAVE_NFTW/HAVE_FTW and uses libc header ftw.h. But it leaves the
codes in lib.c which let mdadm command call nftw defined in lib.c. It
needs to remove these codes.

This problem is introduced by the backport for rhel9.7 (MR is https://gitlab.com/redhat/centos-stream/rpms/mdadm/-/merge_requests/46). And the mdadm version is mdadm-4.4-1.el9. But the package hasn't been released, the test build package can be found at https://kojihub.stream.rdu2.redhat.com/koji/taskinfo?taskID=5686445

The bug can be reproduced by:
mdadm -CR /dev/md0 --level raid5 --metadata=1.1 --chunk=32 --raid-disks 3
--size 10000 /dev/loop1 /dev/loop2 /dev/loop3
mdadm /dev/md0 --grow --chunk=64
mdadm: /dev/md0: cannot open component unknown