[FEATURE] remove notebook unit-tests about recommenders HOT 2 CLOSED

The unit tests in notebooks cover the basic work of the notebook. It is actually an innovation we introduced, in a similar way that unit tests in functions make sure that the function works properly, the unit tests in notebooks make sure that they work.
In the case of functional tests, we are not only checking that the notebooks work, but also that they provide the right values.

For example, a notebook that outputs an RMSE of -1 will pass the unit test because the notebook works, but the functional notebook will break because an RMSE of -1 is incorrect.

The smoke test is just a guardrail for functional or integration tests that take too long, and they go sequentially with the functional test. If a functional test takes 1h runing for 10 epochs, we have a smoke test that is the same notebook but maybe runs for 1 epoch. They are used to check for quick errors.

Consider that the test pipeline we have is not only used for making sure that the repo is healthy but to showcase a pattern in machine learning projects.

We reviewed the categories even with Eric Gamma, who was the creator of junit.

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Closing this, feel free to open to open if needed

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