Cleanup the old counters environment

The counters are in production since a few months now and no issues were detected.

The old counters stack can be decommissioned.

After a discussion, we (sysadms) have decided to keep the counter computation in database and the export to prometheus to have a idea of the drift of the hyperloglogs counters.

However, some tasks are still needed:

• Reduce the refresh of the database counter to once a week or month to reduce the pressure on the database
• Cleanup the puppet code relative the plumbing around stats.softwareheritage.org (script, crons, historical data)
• Cleanup apache the configuration to remove the unused stats.softwarehritage.org vhost
• Remove the files on pergamon

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Migrated from T3417 (view on Phabricator)