Remove `ignore_column` statement in `sbom_occurrences` model

What does this MR do and why?

This MR remove the ignore_column as step 3 of the 3-M drop column process

All of the columns mentioned in this ignore_column have been dropped in %16.9 as part of !142646 (merged)

postgres.ai check

Running \d+ sbom_occurrences shows that the columns in the ignore statement do not exist on the table anymore:

    ignore_column :vulnerabilities, remove_with: '16.6', remove_after: '2023-12-16'

\d+ sbom_occurrences

MR acceptance checklist

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Related to #439315 (closed)