Delete travis ci config file (#6361)

Travis CI is no longer being used.

.travis.yml

@@ -1,27 +0,0 @@
-branches:
-  only:
-   - master
-   - release
-language: python
-python:
-- '3.5'
-before_script:
-- if [ -n "${GH_TOKEN}" ] && [ "${TRAVIS_BRANCH}" == "master" ] && [ "${TRAVIS_PULL_REQUEST}" == "false" ]; then
-    pip install pygithub;
-    pip install pygithub3;
-  fi
-script:
-- python3 tools/sqf_validator.py
-- python3 tools/config_style_checker.py
-env:
-  global:
-  - secure: cdxkn5cAx+s1C9Ne5m+odEhde1uuSg6XGMDgepN4DwSAJwtMnUv3ZmDebd5YJC1raZJdep+n09Cj0GoTNICQRkco50DxHKHYNad41wetY0tn0cs9gmPYzyFE5q4vuWiQ47dlGhQQ7IJDyX0nU++gG5E50/PhlZfebdedGSprN/4=
-notifications:
-  slack:
-    rooms:
-     - secure: byZMNBl8PMlgjT9NA1WmhgCdGfX4b3g1kA0vEiwfm+IFNlx7BiM4J/5rp6zV/jV470xl/epAejx2tsa5SdTyFbO87NH63ILJSt5QnjUZjRuGKSutFs9WE671DtZkPRSJXHS4N6x802PRkyBz/84/lsc34FWvHvjwOuYAtOcJRFk=
-     - secure: V22TNaLWV+yUNWqR7c6HVvIxkRDz7Dyz9xqa43FY8iFgvNL4Q/X69h5DYHU/ILNFM00tx8OBjtPRbcjWQ+F6eY8Sje/A2axJAU+qNurAvoyiTahXUprdUUpPdkgXWuSRTZ9kALxOq5e11RC8XUietghoMcl8zPcqdrZCOOKgoEM=
-    on_success: change
-  email:
-    on_success: never
-    on_failure: change