Polar bear spawn eggs spawn baby polar bears

When using a polar bear spawn egg on a polar bear, it creates baby polar bears. This behavior is not in line with how it is supposed to work, as noted by the resolution of MC-2871. Since polar bears can not be bred by any means in game, they do not fit the requirements for their spawn egg to have such a behavior (only breedable mobs fit the requirements). Update: This also affects zombie horse spawn eggs and skeleton horse spawn eggs.