Deprecate mechanical

BUR #11842 has been approved by @evazion.

deprecate mechanical

Ambiguous tag.

Also came across mechanical bull, mechanical horse, and mechanical bird while making the disambiguation wiki for mechanical. Should these tags be aliased to robot_* for consistency with robot dog and robot_animal, or just merged into robot animal altogether?
There's also mechanical dragon but I'm not sure if that one should also get lumped into mechanical animal as well.

Traditional mechanical bulls definitely shouldn't be lumped in with other robotic animals. Half the time they're just the torso, and they're certainly not autonomous. The rest could probably be renamed, but I don't have any strong feelings on it.

The bulk update request #11842 (forum #219615) has been approved by @evazion.