Remove documentation pages already contained in new doc repository

[ClemensLinnhoff]

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Documentation pages are removed, that are now included in the new documentation repository. It builds the new documentation at https://openmsl.github.io/doc/

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[jdsika]

traffic participant template got lost in the links

[jdsika]

I guess CONTRIBUTING etc needs to stay in this .github repo? What about the things in this doc folder? Should we move this as well to the doc repository?

[ClemensLinnhoff]

traffic participant template got lost in the links

I re-added it

[ClemensLinnhoff]

I guess CONTRIBUTING etc needs to stay in this .github repo? What about the things in this doc folder? Should we move this as well to the doc repository?

Yes, Contributing etc. needs to stay here, because GitHub automatically finds and links it.

In the doc folder only the integration test readme template remains. I would leave it here, since other templates, e.g. for pull requests and issues, are also in the .github repo. It is linked from the documentation and from the readme in the model template repo.