rayzzz: The easiest way to remove units is to give them the no_custom attribute in export_descr_units.txt (that removes them from the custom battle line-up) and then remove the recruit lines from export_descr_buildings.txt (that makes them untrainable. You might also want to go through descr_strat.txt and remove them from the starting units.
If you delete the unit entry in export_descr_units.txt then things are much messier.
Arcani will be gone from the next release. Head Hurlers will be gone when the Britons go. Druids will stay. Is there anything else that needs to be cut?