Clean up unused docker file and image references (#326)

fedora:32 is long since dead, and so is centos:6. Cleaning up the noise
in our lists. We can always git revert if we need them back for some
reason.
17 files changed
tree: 4d262217fb789fbdd4b3ac2c4f0999798e35ecbf
  1. abi/
  2. bin/
  3. docker/
  4. jenkins/
  5. README.md
README.md

trafficserver-ci