Modifies DelayedWETH.unlock so that it can be called while the
system is paused. Same change was recently applied to the specs.
Idea behind this change is that the unlock() function is required
for a game to resolve, so pausing the system would also block
games from resolving. We want games to be able to resolve, we
simply don't want incorrectly resolved games to be able to remove
ETH from the contract. As unlock does not distribute any ETH, this
change is considered safe.