fix #137 and #181 (faulty ROC AUC scores)

[robinruff]

Matbench Pull Request Template

Core code/data/docs changes

Brief description of changes

Fix for issues #137 and #181 (Faulty ROC AUC scores, caused by discretized probabilities).
Removal of the homogenize_clf_array function in data_ops.py as it is no longer used.

Tests

Tests have been changed accordingly.
Test for homogenize_clf_array was deleted, because the function does not exist anymore.
Test for score_array has been corrected.

Closed issues or PRs

Issues: #137, #181

[ardunn]

Great, thanks for the PR! I will review and merge soon

[ardunn]

As a point of discussion, are there thoughts on using F1 as a replacement for ROCAUC for the leaderboards? Since many of the algorithms only have discretized probability $\in {0,1}$

[ardunn]

@hrushikesh-s @computron thoughts on this?