This PR makes sure all sample configs in bin/configs/unmaintained/, including bin/configs/unmaintained/openapi3/, can be generated.

With this goal, I made the following changes:

• removed unmaintained configs for generators that don't exist anymore
• for generators that have been renamed, adapt config accordingly
• fix a bug in the Eiffel generator:
  The generator failed with a NullPointerException for the unmaintained eiffel sample config. Because it couldn't find a certain schema. And it couldn't find it because it looked it up by its lower-case name, instead of using the unaltered capitalization.
• remove samples not generated (anymore) by any config
• remove build instructions for two samples from pipelines, as I deleted these samples

After this PR, ./bin/generate-samples.sh bin/configs/unmaintained/openapi3/*yaml && ./bin/generate-samples.sh bin/configs/unmaintained/*yaml succeeds.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (6.3.0) (minor release - breaking changes with fallbacks), 7.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.
  @jvelilla