Remove 8.5 versions from release/ Ci/ renovate

[hisImminence]

With the 8.8, the 8.5 version is not in standard support anymore and we can remove it from the release flows, CI and renovate updates.

We still need to keep the folders as we must be able to release in case of customers requests with extended support.

[jessesimpson36]

Already done in the HC:

camunda-platform-helm/charts/chart-versions.yaml

Line 11 in 84b9cde

- "8.5"

In docker compose automatic test runs for 8.5 is already disabled:

https://github.com/camunda/camunda-distributions/blob/7b08406e21b6dc25e0195457f2084d2e5b10f437/.github/workflows/docker-compose-test-e2e-full-setup.yaml#L52

C8Run was not supported in 8.5

So I think this ticket can be closed.