[8.12] [ci] Remove ubi8 step (#174257) (#174263)

# Backport

This will backport the following commits from `main` to `8.12`:
- [[ci] Remove ubi8 step
(#174257)](#174257)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT
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Remove ubi8 step (#174257)\n\nUBI8 builds were removed
in\r\nhttps://github.com//pull/173873, but I missed the CI
step\r\nthat verifies the docker context. This removes the
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Remove ubi8
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Remove ubi8 step (#174257)\n\nUBI8 builds were removed
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Remove ubi8 step (#174257)\n\nUBI8 builds were removed
in\r\nhttps://github.com//pull/173873, but I missed the CI
step\r\nthat verifies the docker context. This removes the
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Co-authored-by: Jon <jon@elastic.co>

.buildkite/pipelines/artifacts.yml

@@ -51,16 +51,6 @@ steps:
         - exit_status: '*'
           limit: 1
 
-  - command: KIBANA_DOCKER_CONTEXT=ubi8 .buildkite/scripts/steps/artifacts/docker_context.sh
-    label: 'Docker Context Verification'
-    agents:
-      queue: n2-2
-    timeout_in_minutes: 30
-    retry:
-      automatic:
-        - exit_status: '*'
-          limit: 1
-
   - command: KIBANA_DOCKER_CONTEXT=ubi .buildkite/scripts/steps/artifacts/docker_context.sh
     label: 'Docker Context Verification'
     agents: