Remove`ci.gitlab.com` from haproxy

We no longer need ssl configuration for ci.gitlab.com, this can be removed from the haproxy cookbook.

Original description:

According to @jarv, our HAproxy configuration for GitLab.com includes a section for the domain name ci.gitlab.com

This has no counterpart in gprd and no entry in the DNS.

Does it require any action for the GCP Migration or can we assume it's obsolete and remove the HAProxy configuration currently on GitLab.com ?

/cc @jarv