Remove unused coverity pipeline from 5X_STABLE

concourse/pipelines/pipeline_coverity.yml

-resources:
-- name: gpdb_src
-  type: git
-  source:
-    branch: {{gpdb-git-branch}}
-    uri: {{gpdb-git-remote}}
-
-- name: centos-coverity
-  type: docker-image
-  source:
-    repository: pivotaldata/centos-coverity
-    username: {{docker_username}}
-    password: {{docker_password}}
-
-- name: coverity_daily
-  type: time
-  source:
-    location: America/Los_Angeles
-    days: [Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday]
-    start: 4:00 AM
-    stop: 5:00 AM
-
-jobs:
-
-- name: coverity_scan
-  plan:
-  - get: coverity_daily
-    trigger: true
-  - aggregate:
-    - get: gpdb_src
-    - get: centos-coverity
-  - task: scan_with_coverity
-    file: gpdb_src/concourse/tasks/scan_with_coverity.yml
-    image: centos-coverity
-    params:
-      IVYREPO_HOST: {{ivyrepo_host}}
-      IVYREPO_REALM: {{ivyrepo_realm}}
-      IVYREPO_USER: {{ivyrepo_user}}
-      IVYREPO_PASSWD: {{ivyrepo_passwd}}
-      COVERITY_TOKEN: {{coverity_token}}
-      COVERITY_EMAIL: {{coverity_email}}