Cyanide kills by rendering metalloenzymes inactive. Its principal toxicity probably results from inactivation of cytochrome oxidase (cytochrome aa3) and, thus, cellular respiration. Cytochrome oxidase is the terminal enzyme of the mitochondrial respiratory chain, one of the basic metabolic pathways of life, the one that burns oxygen to create energy. Yeast, humans and all animals use the same respiratory system. (NOTE: the last part of this metabolic pathway works in anaerobic (no oxygen) conditions, too.) Hence I would think that cyanide would kill yeast.

I think it would be terrible mistake to use cyanide in the beer making process since you would have a very good chance of killing yourself with cyanide poisoning while making or drinking the beer. You should use sodium metabisulphite or bleach or boiling water, or other relatively harmless methods to kill your yeast. Don't use cyanide.