[DOCS] Remove reference to platinum Docker image (#30916)

Author: Toby McLaughlin

x-pack/docs/en/setup/docker.asciidoc

@@ -40,7 +40,6 @@ Docker images can be retrieved with the following commands:
 ["source","sh",subs="attributes"]
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 docker pull {docker-repo}:{version}
-docker pull {docker-repo}-platinum:{version}
 docker pull {docker-repo}-oss:{version}
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