Cleanup offer_email_reset associated database columns

As a follow up to the following issue: https://gitlab.com/gitlab-org/gitlab/-/issues/550449, we are planning to remove database columns associated with the "offer_email_reset" feature (ie email_reset_offered_at) that has now been fully deprecated and removed from the codebase.

In accordance with GitLab’s Database Column Removal Process, dropping a column is a multi-step procedure spread across several releases to ensure zero downtime and safe deployment. The general sequence involves:

1. Ignore the column using ignore_column to remove it from the application layer while preserving it in the database.
2. Drop the column in a subsequent post-deployment migration, after confirming it is no longer accessed.
3. Remove the ignore_column directive in a future release once the column has been successfully dropped from all environments.