PyMuPDF replaced the need for almost all dependencies, which this commit
now removes.
We are also removing tesseract-ocr as a dependency since
(to our surprise) PyMuPDF ships directly with tesseract binaries [1].
However, now that tesseract-ocr is not available directly as a binary
tool, the `test_ocr.py` needed to be changed.
Fixes#658
[1]: https://github.com/freedomofpress/dangerzone/issues/658#issuecomment-1861033149