Since the introduction of the patrol feature, the patrol icon has been visible for sheep, even though animals can't patrol. The button should be hidden without hardcoded animal checks.
However we might want to disable patroling of some templates selectively and some mods or maps might want to add patroling animals, f.e.:
From https://en.wikipedia.org/wiki/Lion
The males associated with a pride tend to stay on the fringes, patrolling their territory
Changing the ANIMAL UnitAI state to work with patroling is not in the scope of this diff.
The new CanPatrol boolean is used to disable patroling of traders, fishing ships the hawk and to fix the GUI button of domestic animals without hardcoded checks in the simulation or GUI.