Remove the obsolete ecal related code. #1756 @0.5h

Remove the ecal directory and the directory with the ecal data classes. Adapt the build system accordingly. Closes #1756 @0.5h

I had to create a new merge request since I forgot to put the Redmine related text in the commit message. @v.friese please check if you are properly informed about the merge request and try to merge the request when the pipeline has finished successfully.

changed title from Remove the obsolete ecal related code to Remove the obsolete ecal related code. #1756 @0.5h

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resolved all threads

merged