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.
Then the other test need to be fixed too.
```ruby
before do
  @previous_redis =  Sidekiq.redis
  Sidekiq.redis = REDIS
 ...
end

after { Sidekiq.redis = @previous_redis }
```
I think we should use REDIS.current for thread safety