No-op label column add DB migration

What does this MR do and why?

No-ops a migration introduced in !127683 (merged) that caused a deployment block incident gitlab-com/gl-infra/production#16134 (closed)

See the reasoning for the error in #421145 (comment 1502178641)

we run migrations on Canary, then wait a few hours before rotating pods for Main stage.

So Rails pods on main stage will have cached columns lists, which will not match the list returned by attributes. attributes gets the list by making a database query.

MR acceptance checklist

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

Related to #421145 (closed)