We have removed them. These changes are listed below. The function minibuffer-window no longer accepts a frame as argument, since frames as objects do not exist in Emacs version 18. It returns the window used for minibuffers. There are no overlays, and no faces.
Display tables no longer exist.
The big news about input events is that we got rid of function key and mouse events. Now the only input events are characters. What's more, these characters now have to be in the range of 0 to 127, optionally with a meta bit. This makes for big simplifications. Likewise, a keyboard macro's definition can only be a string, not a vector.