Remove python-us dependency

[dorisjlee]

Overview

Remove python-us dependency due to dependency errors on the lux-api conda feedstock (python-us:56).

[codecov]

Codecov Report

Merging #386 (7a8088d) into master (48b988a) will decrease coverage by 0.15%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master     #386      +/-   ##
==========================================
- Coverage   84.89%   84.73%   -0.16%     
==========================================
  Files          52       52              
  Lines        4031     4035       +4     
==========================================
- Hits         3422     3419       -3     
- Misses        609      616       +7     

Impacted Files	Coverage Δ
lux/vislib/altair/Choropleth.py	84.28% <88.88%> (-9.66%)	⬇️

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