MNT: Remove unused astropy config code

[pllim]

This is probably leftover from package template. This package does not use the astropy configuration system at all.

Also see astropy/astropy#11497

[codecov]

Codecov Report

Merging #338 (4c621f3) into main (120e756) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #338   +/-   ##
=======================================
  Coverage   91.86%   91.86%           
=======================================
  Files          33       33           
  Lines        2508     2508           
=======================================
  Hits         2304     2304           
  Misses        204      204           

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