BLD: fix readthedocs

[UranusSeven]

What do these changes do?

Remove the unused matplotlib extension from extension list.

Related issue number

Check code requirements

• [x] tests added / passed (if needed)
• [x] Ensure all linting tests pass

[codecov[bot]]

Codecov Report

Merging #29 (fda0e96) into main (a759da3) will decrease coverage by 3.74%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
- Coverage   91.02%   87.29%   -3.74%     
==========================================
  Files          42       42              
  Lines        3187     3187              
  Branches      638      638              
==========================================
- Hits         2901     2782     -119     
- Misses        212      340     +128     
+ Partials       74       65       -9     

Flag	Coverage Δ
unittests	87.19% <ø> (-3.64%)	:arrow_down:

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see 8 files with indirect coverage changes