Changed pint.ls to astropy.u.lsec

[dlakaplan]

Astropy added a light-second unit years ago. I think rather than defining our own (which used astropy's definition of c) we should use their version throughout.

This might break some downstream software, so if needed we could put back the definition of pint.ls = u.lsec, although we do use the pint_units as keys for string parsing which includes ls.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.39%. Comparing base (f5dfaf6) to head (f3d877a).
⚠️ Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2008      +/-   ##
==========================================
+ Coverage   70.32%   70.39%   +0.07%     
==========================================
  Files         109      109              
  Lines       25745    25743       -2     
  Branches     4106     4107       +1     
==========================================
+ Hits        18105    18122      +17     
+ Misses       6473     6450      -23     
- Partials     1167     1171       +4     

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[abhisrkckl]

This looks good. I will merge this if ready.

[dlakaplan]

This looks good. I will merge this if ready.

Yes, once the latest merge finishes.