Remove redundant Travis CI config

[hugovk]

The badge was removed from the README in 2020: f852e6a

https://travis-ci.org/jquast/wcwidth says "We couldn't display the repository
jquast/wcwidth".

Let's remove the old config file.

[jquast]

Thanks @hugovk

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (cd64438) to head (46300f0).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #143   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          109       109           
  Branches        21        21           
=========================================
  Hits           109       109           

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