Revert 65bb88ed, incident 4569

What does this MR do?

This reverts !61435 (merged), renaming the migration scripts with the 2021 timestamps.

Note: I've reverted 65bb88ed and created a separate commit to change the timestamps to 2021 but I was not able to push the two commits:

remote: Checking connectivity: 86, done.
remote: GitLab: File name db/migrate/20260421104929_add_epic_board_recent_visits_table.rb was blacklisted by the pattern ^db\/migrate\/2026.
To gitlab.com:gitlab-org/gitlab.git
 ! [remote rejected]         incident-4569 -> incident-4569 (pre-receive hook declined)
error: failed to push some refs to 'gitlab.com:gitlab-org/gitlab.git'

So, I've squashed the two commits into one.

Related gitlab-com/gl-infra/production#4569 (closed).

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