I was confused, actually, not you. The output was:
cat /sys/dev/block/8:176/queue/scheduler
[mq-deadline] none
However, this output does not mean what I thought it did - it means that mq-deadline is in use.
If I do
echo "none" | sudo tee /sys/dev/block/8:176/queue/scheduler
This changes to
cat /sys/dev/block/8:176/queue/scheduler
[none] mq-deadline