Remove development regression model files

[JamesPino]

There are currently multiple files for the regression models.

run_all.py
run_all_kfold_ultimate.py
run_gbt_kfold.py
run_lightgbm.py
run_models.ipynb

Basically they were built via sequentially increasing complexity, but all are summarized in run_all_kfold_ultimate.py and run_all.py, though the latter is a dumbed down version without features as output. run_models.pynb is worth keeping as it contains a lot of visualization of model performance, something that isn't stored in the other two run files. I am making this issue here for now to remember to remove the old ones once we decide on where to place the model figure folder.