Remove our edc-connector build directory and replace it with upstream versioned build

[fhennig]

We do not want all this Java stuff in here, this was only because at the time there were no build artifacts available in the upstream project.
Now it would be good to switch.
This might be a lot of work because we will also have to update to the latest EDC version, and there will probably be many breaking changes.

Upstream project: https://github.com/eclipse-edc/Connector

Difficult could be to somehow get the IONOS extension in? It wasn't adopted upstream: eclipse-edc/Connector#3006 - Extension repo: https://github.com/ionos-cloud/edc-ionos-s3