Remove deprecated continuous onboarding route

What does this MR do and why?

• route removed in %15.9 and only reached on .com.

logs to watch for old path: https://log.gprd.gitlab.net/goto/5fede250-aee6-11ed-9f43-e3784d7fe3ca

From the logs above for a few still having this in their redirect/history path it is failing since we never provided the namespace path correctly. So removing it now for those few remaining requests will not have any impact.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #390715 (closed)