Remove `sbom_occurrences` from PreventIndexCreation cop

What does this MR do and why?

With the completion of https://gitlab.com/gitlab-org/gitlab/-/issues/442486, the update rate for this table has dropped to near-zero levels.

source

We can also see that queries matching the fingerprint e2af01a08d80303e have dropped completely off the charts for pg_stat_statements_wal_bytes. This is because the stats are limited to the queries with the highest WAL rate.

source

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.