Remove all `embeddings` database config from GitLab/CNG/Omnibus

Related to gitlab-com/gl-infra/data-access/dbo/dbo-issue-tracker#333 (closed) we are no longer using the embeddings database anymore and it contains no tables. But there is still code in GitLab/CNG/Omnibus which references this database. This has a maintenance cost as all code which touches DB connections needs to look at it and reason about how their change will impact things.

We can remove the config and deprovision the production database before we remove the code from GitLab but we should still remove the code from GitLab to simplify future maintenance.