Deprecate dependencies combination FS apr21p2 + FR v18.6.7

• Remove the Debian/vae CI jobs for this pair
• Change OLD versions in autoinstall script to FS nov22p1 + FR v18.8.0
• Update README

Still Needed before removing draft mode:

• Not removed in CI => Done
  • macosx_1015 Old
  • macos11 Old
  • macOS12 Old
• Missing in CI => To be addressed later (see !2188 (comment 55507))
  • macosx_1015 Pro and Dev
  • macos11 Dev`
  • macOS12 Dev`

To be updated out of the MR:

• Weeklies kn04 debian10-linux-x86_64-gcc8-Weekly-fairsoft_apr21p2-fairroot_v18.6.7

Redmine: Also addressing Ref #3163 "Deprecate Fairsoft Apr21 as it contains a bug with TWebBrowser/TWebCanvas"

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@f.uhlig: if we just keep the number of jobs in the CI constant, I guess we could

• replace the Old with a Pro for macosx_1015
• replace the Old with a Dev for macos11 and macos12