Add uprating factors generation to the Makefile and remove uprating factors csvs from repo

[baogorek]

The checked in files uprating_factors.csv and uprating_growth_factors.csv can be generated by running policyengine_us_data/utils/uprating.py. Having the file checked in implies that it comes from some other source, or is edited by hand (which I was doing before I noticed the file). As make data is already a step that populates the storage directory with dynamically generated files, my recommendation is to:

• git remove these files and add them .gitignore
• add the uprating.py script to make data
• add the uprating csvs to make clean

When I get back to PR #211, this would be easy to add. Please advise.