Remove kwonly as @jni's suggestion

[hmaarrfk]

@jni

this is the start.

[codecov]

Codecov Report

Merging #20 into master will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   93.70%   93.77%   +0.06%     
==========================================
  Files          10       11       +1     
  Lines         556      562       +6     
==========================================
+ Hits          521      527       +6     
  Misses         35       35              

Impacted Files	Coverage Δ
wabisabi/__init__.py	100.00% <100.00%> (ø)
wabisabi/kwonly_change.py	100.00% <100.00%> (ø)
wabisabi/update_keyword_only.py	100.00% <100.00%> (ø)

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