Remove EPEL 6 from the build matrix

.gitlab-ci.yml

@@ -67,23 +67,6 @@ upload/epel/7:
   <<: *upload
   dependencies:
     - build/centos/7
-
-build/centos/6:
-  <<: *build
-  variables:
-    DOCKER_IMAGE: centos/6
-
-test/centos/6:
-  <<: *test
-  variables:
-    DOCKER_IMAGE: centos/6
-  dependencies:
-    - build/centos/6
-
-upload/epel/6:
-  <<: *upload
-  dependencies:
-    - build/centos/6
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 # Fedora
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