If the tasks scheduled by ForkJoinPool are all busy and new task is
added, the pool would throw RejectedExecutionException if the "saturate"
Predicate is not specified.

To avoid that, supply Predicate that is always true - with that, no
exception will be thrown on busy pool and we would not reject new delete
operations.

Fixes https://github.com/eclipse-platform/eclipse.platform/issues/1592