vdev: skip faulting disks pending removal

This patch fixes a race where vdev_remove_wanted may be set after probe
initiation, which could otherwise trigger redundant fault and removal.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #17400