mint-arena: Remove unused function ClientSkin
mint-arena: Add more optional bubble effects

Set cg_oldBubbles 0 to enable new bubble effects

- Make projectile bubble trails more faster to surface and last longer.
- Add bubble breath puffs (based on Team Arena cold breath puffs).
- Add bubbles to gib effect when it player is underwater.

The first two are based on Turtle Arena, though I made bubbles rise faster.