This removes the 'deterministic test' tools by preventing action at a
distance (namely, preventing the modification of the `init` method in
`Battle` during tests). This action at a distance is incredibly
confusing.
All this action at a distance did was discard any parameters that were
passed to `Battle` that weren't the first three (which was probably a
mistake by the original author) and also hard code `this.seed` and
`this.startingSeed` in `Battle`.
This functionality has now been moved to the `PRNG` class, so instead
users should pass a `PRNG` to `Battle` as the 5th constructor argument.
Users can also pass one as the third argument to `common.createBattle`
or use `common.createBattleWithPRNG` with the PRNG as the first
argument.
The PRNG is just an encapsulation of the pseudo-random algorithm in a
class. It is stateful, so make sure to take a `clone()` of the PRNG if
you want to re-use it.
