remove centos 6 build

- centos 6 has reached end-of-life

codeship-services.yml

@@ -6,14 +6,6 @@ deb:
     - ./tmp:/artifacts
   encrypted_env_file: build.env.encrypted
   cached: true
-el6:
-  build:
-    dockerfile_path: ./installers/build/Dockerfile.el6
-  volumes:
-    - .:/src
-    - ./tmp:/artifacts
-  encrypted_env_file: build.env.encrypted
-  cached: true
 el7:
   build:
     dockerfile_path: ./installers/build/Dockerfile.el7

codeship-steps.yml

@@ -39,9 +39,6 @@
         command: /src/installers/build/fetch_client.sh linux64
       - type: parallel
         steps:
-        - name: Build EL-6 installer with desktop
-          service: el6
-          command: /src/installers/rpm/build.sh 6 --with_client
         - service: el7
           name: Build EL-7 installer with desktop client
           command: /src/installers/rpm/build.sh 7 --with_client
@@ -64,9 +61,6 @@
     - service: deb
       name: Build MacOS installer
       command: /src/installers/osx/build.sh
-    - service: el6
-      name: Build EL-6 installer
-      command: /src/installers/rpm/build.sh 6
     - service: el7
       name: Build EL-7 installer
       command: /src/installers/rpm/build.sh 7