release-23.2: sql/schemachanger: clean up SequenceOwner elements during restore

[blathers-crl]

Backport 1/1 commits from #132202 on behalf of @fqazi.

/cc @cockroachdb/release

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Previously, when restoring a backup taken in middle of a DROP COLUMN, where a column had a sequence owner assigned, it was possible for the backup to be unrestorable. This would happen because the sequence reference would have been dropped in the plan, but the seqeunce owner element was still within the state. To address this, this test updates the rewrite logic to clean up any SequenceOwner elements which have the referenced sequence already removed.

Fixes: #130778

Release note (bug fix): Addressed a rare bug that could prevent backups taken during a DROP COLUMN operation with a sequence owner from restoring with the error: "rewriting descriptor ids: missing rewrite for in SequenceOwner..."

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Release justification: low risk fix for an issue that would prevent certain backups from being restored, if the backup was taken during a DROP COLUMN for a column that is a sequence owner.

[blathers-crl]

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[blathers-crl]

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[cockroach-teamcity]

This change is 

[Dedej-Bergin]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @fqazi and @rafiss)

[fqazi]

Sadly this backport doesn't work because the rules differ a lot on this branch. On this release we also have the Namespace entries left behind for the same Sequence during the dropped state, so those have to be re-written too. Among probably a lot of other things. So, for simplicities sake we aren't going to backport the fix to this branch.