refactor: remove migration application

[ChrisKujawa]

Which problem does the PR fix?

Removes obsolete migration application. Was already removed here https://github.com/camunda/camunda/pull/24620

What's in this PR?

Remove the config and init-container

Checklist

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[ChrisKujawa]

So to me it looks like this PR is obsolete right? @houssain-barouni @aabouzaid there is no migration app as init container anymore in the core statefulset.

[aabouzaid]

@ChrisKujawa that's correct. No migration int container for Core so far.