tools: remove obsolete test tooling + add CI badge (#3555)

* tools: remove obsolete test tooling
- tests should now be performed from https://github.com/awesome-selfhosted/awesome-selfhosted-data#maintenance
- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/1038
- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/1852
- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2266
* add a badge pointing to the main issue about unmaintained projects/dead links removal
- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2266

.github/CONTRIBUTING.md

@@ -8,7 +8,6 @@ Other recommendations:
 
 - To add a new entry, [edit the README.md file](https://github.com/awesome-selfhosted/awesome-selfhosted/edit/master/README.md) through Github's web interface or a text editor, and send a Pull Request.
 - See [Editing files in another user's repository](https://help.github.com/articles/editing-files-in-another-user-s-repository/), [Creating Pull Requests](https://help.github.com/articles/creating-a-pull-request/), [Using Pull Requests](https://help.github.com/articles/using-pull-requests/) for help on sending your patch.
-- A script to help you format new entries is available at (it requires `make` to be installed): `git clone`/[download](https://github.com/awesome-selfhosted/awesome-selfhosted/archive/master.zip) and enter the repository, run `make add` and follow the instructions.
 - A website to help you format new entries is available at https://n8225.github.io/
 - The list of contributors can be updated with `make contrib`. 
 - Software with no development activity for 6-12 months may be removed from the list.