Handle uncancellable timeout future more reliably.
Revert "Added new option jruby.timeout.thread.pool.max to control the max number of Timeout worker threads."

This reverts commit 8bbe14b9a3483ff9a789f56cc3a4beeb7446a18e.

The first parameter to newScheduledThreadPool is not a max, it is
a minimum. That makes the original commit moot, since it does not
limit thread count and actually causes more threads to be alive
than are necessary.