Remove conditions on 2 User email validations

What does this MR do and why?

The User model had 2 validates declarations for secondary email attributes that had unnecessary conditions. This removes those conditions. At most they offered a negligible performance improvement, at the cost of adding complexity to secondary emails, which are security-sensitive and should be kept as simple as possible.

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 https://gitlab.com/groups/gitlab-org/-/epics/6564