Select base monsters so that only spawn fast zombies in D

Slow monsters are bad for a variety of reasons, most notably heavily
encouraging kiting and always allowing the player to flee.
Revert "Reduce the numbers of derived undead in late D"

Since 8a682ed7d just buffed zombies, hopefully making them more relevant
in late D.

This reverts commit f7beed7a6853614331b316f3cc403ec32d90b920.