Remove Travis CI and AppVeyor config

[hugovk]

Looks like they're no longer used.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.97%. Comparing base (efb2043) to head (8c8ab97).
⚠️ Report is 43 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #269      +/-   ##
==========================================
- Coverage   95.21%   94.97%   -0.25%     
==========================================
  Files           2        2              
  Lines        1819     1909      +90     
  Branches      177      177              
==========================================
+ Hits         1732     1813      +81     
- Misses         43       52       +9     
  Partials       44       44              

Flag	Coverage Δ
unittests	94.76% <ø> (-0.41%)	⬇️

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