chore(ci): remove nightly CircleCI workflow

[cannonpalms]

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• chore(ci): remove nightly CircleCI workflow (f6e1b88)

  This project is no longer maintained and all downstream consumers have
  been retired, so the nightly build serves no purpose.
  
  Drops the `nightly` workflow along with the `scheduled_pipeline` guard on
  `build`, which only existed to keep the two workflows from both running
  on a scheduled trigger.
  
  Note that the schedule itself lives in CircleCI project settings, not in
  this file, and must be deleted separately from the Triggers page.
  

[jdstrand]

I deleted the nightly trigger using my admin account directly in circle by using https://app.circleci.com/settings/project/github/influxdata/nifi-influxdb-bundle/setup and deleting the appropriate pipeline. I'm going to commit this before archiving (I'd like to see how CircleCI responds).

[jdstrand]

Note for posterity, 'Overview' has a 'Stop Building' button that seems like it would be good to do on any archived repo.