This patch simplifies the `template_unit_ship*` files by removing unnecessary lines:
* <Cost>, <Health/Max>, <Loot>, and <Vision> are removed from the shared parent because they're superseded in practically all its children.
* <GarrisonHolder> is moved into the shared parent, because it was defined in most its children (except the fireship).
* <Footprint> is moved to the specific `units/*` files that don't have footprint values yet, since different units use different actors of different sizes.