travis-ci: remove Ubuntu Eoan

Ubuntu Eoan is EOL and fails in CI on apt repositories updating with
'does not have a Release file' errors.

Author: LeonidVas

.travis.yml

@@ -26,7 +26,6 @@ env:
       - OS=ubuntu DIST=trusty
       - OS=ubuntu DIST=xenial
       - OS=ubuntu DIST=bionic
-      - OS=ubuntu DIST=eoan
       - OS=ubuntu DIST=focal
       - OS=debian DIST=jessie
       - OS=debian DIST=stretch