Remove final mentions of the LUA script

This also means we need to change the basic 'is this thing on?' connection check. PING is the usual suspect. Note that this is not an 'administrative' command in the context of 'redis-namespace', so we can go direct to 'conn' and remove the scary comment.

Without this 11.0.0 is non-functional for sidekiq; it will start up, but throws an error when metrics are fetched:

NameError - uninitialized constant GitLab::Exporter::SidekiqProber::QUEUE_JOB_STATS_SHA: