Remove what's left of setup_dev.sh & setup.sh

[Wumpf]

What

Almost everything has been taken over by pixi by now and these outdated / partially broken scripts keep confusing new-comers to the repo, so at this point they're clearly doing more bad than good.

• Fixes Setup.sh is broken on linux. And lots of things are broken on linux-aarch64 #5545
• Fixes Replace our setup*.sh files with pixi #4170
  • There's still some stuff that should be moved to pixi but that's better covered by Use pixi to replace our bash scripts and many of the Dockerfile layers #3717

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

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[emilk]

Great - thank you!