Delete pyproject.toml

[rabernat]

This may fix #108. Our issue seems similar to SciTools/cartopy#1270 (comment).

@roxyboy - can you explain why you added pyroject.toml and what it does?

[codecov]

Codecov Report

Merging #109 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #109   +/-   ##
=======================================
  Coverage   97.58%   97.58%           
=======================================
  Files           2        2           
  Lines         788      788           
  Branches      125      125           
=======================================
  Hits          769      769           
  Misses         10       10           
  Partials        9        9           

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[rabernat]

I'll try to merge this and issue a new release to see if it fixes things.