[Bug/Unit Design] Created Pioneers cannot be made with no weapons

By default, the normal Pioneer has no weapons

However, if you attempt to modify the design, it's impossible to make a new one without selecting a weapon, so you're always paying more Production cost than a default Pioneer.

Add the ability to remove weapons from Pioneers.

Also, I don't see a Pioneer 'trait', so it's not at all clear that the only way to create new Pioneers is to edit the existing one - this is very unclear for a new player, and should probably be looked at.