Remove legacy CI configuration files

[JeroenDeDauw]

Summary

Drop .travis.yml, .travis.install.sh, and .scrutinizer.yml. TravisCI and Scrutinizer haven't been wired into this repo for years -- CI runs entirely in GitHub Actions (.github/workflows/ci.yml).

• No badge or doc references to update -- the README.md already only points at GitHub.
• The dropped files reference PHP 7.x and MediaWiki <= 1.33; current CI matrix is PHP 8.1+ / MW 1.43+.

Test plan

• CI green

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.16%. Comparing base (26ccc8c) to head (7adddc5).

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #88   +/-   ##
=========================================
  Coverage     93.16%   93.16%           
  Complexity      166      166           
=========================================
  Files            17       17           
  Lines           571      571           
=========================================
  Hits            532      532           
  Misses           39       39           

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