USFEMA_NationalRiskIndex download_url_fix

[kartik-s21]

This PR updates the National Risk Index (NRI) data download script and cleans up tracked CSV data files in accordance with the latest FEMA v1.20 data release.

What was done:

• Updated download links: Modified sh/download_data.sh to fetch the county-level and tract-level NRI datasets from the official FEMA v1.20 endpoints instead of the
  obsolete hazards.fema.gov links.
• Expanded Data Dictionary: Replaced the Git LFS pointer for NRIDataDictionary.csv with the raw CSV text contents for version 1.20.0 (December 2025) to make the field
  descriptions directly readable and accessible.
• Removed large tracked file: Deleted the hardcoded NRI_Table_Counties.csv (which was previously tracked under LFS) to save repository space, as this data is dynamically
  retrieved during the download step.

Why this is needed:
The old download links are no longer functional, causing local data download scripts to fail. Updating them to the OpenFEMA v1.20 archive URLs ensures reliability, and
removing the heavy county-level CSV keeps the repository lightweight.

After that, numerous source side deletions are observed in the differ validation report, for which a document is created addressing all the deletions properly

document link - https://docs.google.com/document/d/1esXHmisK2D9Yx9j_-6x0leRGlhAc18_77DMtzQnahB4/edit?resourcekey=0-h130g3obSJVd_zScRvBYmg&tab=t.0
differ link - https://storage.mtls.cloud.google.com/unresolved_mcf/scripts/us_fema/national_risk_index/national_risk_index/output/dc_generated/differ/obs_diff_log.csv?authuser=0

[gemini-code-assist]

Code Review

This pull request updates the FEMA National Risk Index download URLs to version 1.20 on fema.gov and replaces the Git LFS pointer for the NRIDataDictionary.csv file with its actual CSV content. The feedback recommends adding the -f or --fail flag to the curl commands in the download script to ensure it fails immediately on HTTP errors instead of silently writing error pages to the output files.

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[saanikaaa]

1. I see many data points coming as modified in differ. Can you pls check if we have selected the correct input file. Pls spot check points modification and document your findings.

2. Add PR checklist