Fix issue where explosions do not affect ship buoyancy

[chocbic172]

Fixes issue #308.

Changes:

• Replaced instances of Block::destroy() for BlockBehaviour::remove() for Helm, Floater, Anchor and Balloon blocks. The new method is called any time a block is removed, whereas the old method seemed to only be called when a block was removed by a player.

Run through of reproduction steps to verify:

Steps ran as expected. Note that both ships are on the floor.

[Rubydesic]

Thanks for your contribution, we will review it soon

[millennIumAMbiguity]

Fine, I'll do it myself