dowhy_causal_discovery_example.ipynb notebook is causing failures in nightly build of advanced tests

[emrekiciman]

See https://github.com/py-why/dowhy/actions/runs/2975864094

It looks like the causal discovery toolkit is not being installed --- probably because of its complex dependencies --- and that is causing this advanced test to fail

Given the move towards dodiscover and causal-learn, we should simply remove this test from the nightly builds.