chore(CI CIDRs): remove ephemera-runners obsolete network ranges

Clean up the CIDR list, here are some notes:

1. Removes all references to ephemeral-runners subnetworks, as these are not used any more.
2. Corrects the name of some networks from r-saas- to saas-.
3. Corrects the name of projects from r-saas to gitlab-r-saas.
4. Adds missing CIDR for small-amd64-6.
5. All the IPs that were removed were compared to the IPs in config-mgmt
   • If an IP is mentioned as a variable to an ephemeral environment, it is not used.
   • If an IP is mentioned in the environments/ci/variables.tf file, it is in use.
   • If an IP is mentioned in the gprd firewall allow list, it doesn't necessarily means it is in use (that list needs a cleanup).

ref: gitlab-com/gl-infra/production-engineering#26049 (closed)