Remove pgvector (final part)

What does this MR do and why?

We've removed pgvector from the gitlab repo(gitlab!210182 (merged)), so we can finally remove all the postgres build images with pgvector since they're no longer in use.

Checklist

• (If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.