regenerate 2021 metadata

[damonmcc]

per discussion with Population and Tyler:

• should be using ACS Data Dictionary.xlsx as source of metadata.json
• related to https://github.com/NYCPlanning/db-factfinder/issues/258

changes

• modify ACS Data Dictionary.xlsx to only have the columns OSE will use in (relevant OSE code)
• modify ACS Data Dictionary.xlsx to have lower case values for pff_variable and domain
  • as was done to the json file in #257
• regenerate metadata

[damonmcc]

@TylerMatteo merging this for urgency

[TylerMatteo]

Thanks @damonmcc! Re-running our scripts now.