Remove demo image for 2.0.0 release

[nigelgbanks]

It's basically unmaintained and doesn't work with PHP 8.1, also we're pushing folks towards adopting the start site approach.

[edlington]

@nigelgbanks wondering what this means: "also we're pushing folks towards adopting the start site approach." Is that at the container level? Or at the composer level? Both?

[rosiel]

From discussions at the Tech Call: Long term: it would be good to have a way for new islandora users to:

• simply (e.g. make demo)
• reliably (not failing!)
  spin up an islandora that has some sample content in it.

But using the starter site. It would be good to deprecate the "demo" that uses the install profile (the topic of this ticket)

[nigelgbanks]

I've built out a test image that uses the starter site and has some sample content in it. It's being used by buildkit to run automated tests on pull requests to ensure that derivative generation, etc. doesn't get broken. It could be potentially used.

[nigelgbanks]

Done under #238 Includes a workflow that does this.