Revert "Merge branch 'remove-custom-getter-methods-for-secondary-emails' into 'master'"

What does this MR do and why?

Reverts !69648 (merged)

This is causing isssues with issue and MR creation when the user has a private commit email.

See gitlab-com/gl-infra/production#5549 (closed)

How to set up and validate locally

1. Create / update a user to have a private commit email.

   user.update_column(:commit_email, '_private')

2. Check if model is valid.

   user.valid?

Before

[1] pry(main)> i = Issue.new(project: Project.first, author: User.first, title: 'Test', assignee_ids: [4155490]); nil
=> nil
[2] pry(main)> i.valid?
=> false
[3] pry(main)> i.errors.full_messages
=> ["Assignees is invalid"]
[4] pry(main)> user = User.find(4155490)
=> #<User id:4155490 @marcel.amirault>
[5] pry(main)> user.valid?
=> false
[6] pry(main)> user.errors.full_messages
=> ["Commit email is invalid"]
[7] pry(main)> user.commit_email
=> "_private"

After

[1] pry(main)> i = Issue.new(project: Project.first, author: User.first, title: 'Test', assignee_ids: [4155490]); nil
=> nil
[2] pry(main)> i.valid?
=> true
[3] pry(main)> i.errors.full_messages
=> []
[4] pry(main)> user = User.find(4155490)
=> #<User id:4155490 @marcel.amirault>
[5] pry(main)> user.valid?
=> true
[6] pry(main)> user.errors.full_messages
=> []
[7] pry(main)> user.commit_email
=> "4155490-marcel.amirault@users.noreply.dev.engwan.me"

MR acceptance checklist

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