Delete all testing jupyter notebooks from repo

Review each of the following notebooks for any important differences from their corresponding .py scripts. Once discrepancies are resolved, delete the notebooks:

[ ] clean_merged_data.ipynb
[ ] data_visualizations.ipynb (might keep this one though)
[ ] league_merge_testing.ipynb
[ ] merge_script_testing.ipynb
[ ] player_summary_tables.ipynb
[ ] pre_analysis_vis_testing.ipynb

cmartins2001 / player-valuation-model

Delete all testing jupyter notebooks from repo #5