Smokery still shown under buildings despite Slaughterhouse requirement not met

[NielsCW]

Slaughterhouse requires worked sheep, deer, cattle or horses near the city.

I suggest letting Smokery also require this. Other buildings that depend on a building also copy its city requirements (e.g. Seaport requires being next to coast just like its required building (Harbor) does).

[shannaurelle]

Committed PR and merged.