redundant tests

[jvoigtlaender]

These tests seem to be redundant, based on how/when these functions are called:

• https://github.com/zrho/afp/blob/master/battleships/Logic/Game.hs#L381-382
• https://github.com/zrho/afp/blob/master/battleships/Logic/Game.hs#L399-400

And, BTW, aren't these two functions humanTurnFire and moveHuman rather inconsistently named?