Added method to Util module to clean up process records...

 that don't have a matching heartbeat record, indicating that they're no longer alive.

Added call to this new util method in the `Scheduled::Poller.poll_interval`
method because the number of live processes is used as a multiplier for
the default wait interval.  Since the value for poll_interval is
memoized, this call to 'cleanup_dead_process_records' should only be
called once at startup.
So, I'm not sure what to do here given how `Sidekiq.redis` is implemented.  There isn't a way to tell at this point if `Sidekiq.redis` has a value given that it will automatically create a redis connection if one hasn't been set.

This before block was modeled after the one in `test_scheduled.rb`, which doesn't do anything in an after block either.

Thoughts?