Instructions to enable spidev on DB410C no longer work with 21.12 (and later) releases

[daniel-thompson]

These instructions no longer work.

See https://discuss.96boards.org/t/spidev-on-21-12/11885/2 for more details.

URL: https://www.96boards.org/documentation/consumer/dragonboard/dragonboard410c/guides/enable-spi.md.html