clean dataset more (optional)

[BlairCurrey]

These are uncompleted items from https://github.com/BlairCurrey/swe-salary-predictor/issues/1 which may not be necessary

• [ ] check for multicollinearity problems with one hot encoded features https://www.analyticsvidhya.com/blog/2020/03/one-hot-encoding-vs-label-encoding-using-scikit-learn/
• [ ] move encoding out of initial data loading (do independently on train/test) https://datascience.stackexchange.com/questions/107714/encoding-before-vs-after-train-test-split all? just one hot encoded? this seems to suggest that it wouldn't be a problem for ordinal encoding https://datascience.stackexchange.com/questions/78146/does-label-encoding-an-entire-dataset-cause-data-leakage