Move ammo hud sprites to hud.json

[SamVanheer]

Move ammo HUD sprites to hud.json. They are currently defined in the individual weapon config files.

The HUD looks up the ammo sprites by looking for the first weapon that uses a particular ammo type which can cause discrepancies if multiple weapons use the same ammo type with different sprites.

There is no need for these to be defined by weapons to begin with. Only weapon-specific sprites should be in those config files.