A technical approach to the Quest-topic by Onyx (brilliant as well as enjoyable):

Walking around in the ruins
NOTE: This article consists of theories only, and not proven statements. They are born from the similarity of function of some unused quest and some used quests. They might or might not be true, and most likely we'll never know for sure.

You have all read Trimayne's quest article and you're probably excited about the amount of unused material in Diablo. But did you ever think that when you're heading to find that Black Mushroom again and again and again, you might be seeing all those things in action? This article deals exactly with that. It tries to link the existing quests with the removed ones, because many of them have similar functionality. There goes:

Poisoned-Water Worms:
The removed quest is about the basement of a house in Tristram that is invaded by worms. You must go there and kill them all to complete the quest. Furthermore, a piece of the town changes while the quest is active (the door of the house is open and we can safely assume that it will be closed once you complete the quest). Would have made a wonderful quest in the final version, considering that you were going to enter a new dungeon and fight a new enemy! But wait...
Poinsoned Water Supply... You need to find the passage and kill all the monsters in there in order to finish the quest. Again, an object in town changes – the water in the well becomes yellow-ish while the quest is active and after that is restored to normal. A coincidence?
You decide. The only difference is that the level is not directly attached to town. Dress the new level with a cave tileset, put fallen and stuff inside, rework the speeches and viola! The worms turn into a water supply.

Learn what?
Seems like the whole 'learn-spell-from-a-book'concept was around in the very early days of Diablo. And it appears that there was a Learn Golem book in Horazon's Sanctum. Was that an independent quest? Or was it a reward for completing Horazon's quest? We'll never know. I tend to think that the latter is highly possible.

In the final version we have Chamber of Bone... with a quite similar reward – learn Guardian from a book. It's also known that in previous versions of the Chamber of Bone quest, the book was giving Nova to the player. The spell changes, but maybe the book stays the same. So this book just might be that same book that was supposed to be in Horazon's Sanctum and teach your character Golem.