Have Gozag never create shops of a useless type for the player

Previously Gozag would give Mu food/potion shops, Fe weapon/armour
shops, etc. The list of disallowed shops include the cases mentioned
above and when the player has sacrificed artifice by abandoning Ru,
but there may be others. There are borderline cases like Op and
armour, but Op can use hats and shields, so they can get armour shops
for now. We can make shop content selection in the future (as opposed
to shop type), if that's deemed necessary.