How to remove "Deceased" entries from units list?
Solution 1:
Without using some third-party tool that modified the game in memory, you can't. The unit list will contain everyone.
In recent versions (DF2012), the unit list has been split into tabs. One tab is set aside for all units which are missing/ghostly/deceased.
Solution 2:
While you can't remove them with just normal Dwarf Fortress. I did some research, and I hear that Runesmith might be able to. I've never used it personally. Page Up/Page Down are good enough for me.