calamari_ocr dependency outdated and heavy

[bertsky]

We still have calamari_ocr == 0.3.5 in install_requires. That's quite a drag IMO: it is quite out-dated, pulls in Tensorflow/Keras (themselves outdated), and probably not really necessary (since we've had ocrd_calamari for quite a while now).

Can we remove this?

(I see references to Calamari in div.eval, div.auswerter.runcalamari and aio.runcalamari.)