Replace integration test that uses the iris demo data

[npatki]

Problem Description

The test_tvae integration test currently uses the iris demo dataset from scikit learn.

CTGAN/tests/integration/synthesizer/test_tvae.py

Line 22 in 37cc86c

iris = datasets.load_iris()

However, as of the latest merge, scikit-learn is no longer a dependency of CTGAN. So we shouldn't be using it for any testing. It is better to replace this dataset with a different demo (or potentially a hard-coded one).

Additional context

If we don't require skicit-learn anymore, then why is this integration test still passing? That's because CTGAN requires RDT to run, and RDT requires scikit-learn.

In any case, we'd like to clean up dependencies within each library. Since the functionality of CTGAN doesn't directly need scikit-learn, we should not have it referenced in this repo.