AttemptTimeLimiter does not have to be generic

[james-hu]

public interface AttemptTimeLimiter<V> {
    V call(Callable<V> callable) throws Exception;
}

can be changed to

public interface AttemptTimeLimiter {
    <V> V call(Callable<V> callable) throws Exception;
}

So that we don't have to specify a generic type when creating the Retryer