Witch pack maximum size changed

Witches can no longer spawn in packs in 1.13 and forward. This severely limits the rate that witches spawn at. The way this changed is the maximum pack size for a witch is now 1 instead of 4. Other changes to maximum pack sizes and attempts at a pack were done as well to other mobs.
This further reduces the already rare chance of encountering a witch during normal gameplay by a factor of 2.5.