To completely remove an mdadm raid array you must “zero the superblock” on the component drives, so that mdadm will not detect them on its next scan/reboot of your system:
sudo bash
mdadm --stop /dev/md1
mdadm --remove /dev/md1
mdadm --zero-superblock /dev/sdb3
mdadm --zero-superblock /dev/sdc3
mdadm --stop /dev/md1
mdadm --remove /dev/md1
mdadm --zero-superblock /dev/sdb3
mdadm --zero-superblock /dev/sdc3
Oh…and happy new year!
With thanks to MDLog:/sysadmin.