Remove sbom_occurrence_ref_es_indexing feature flag

What does this MR do and why?

Elasticsearch indexing of SBOM occurrence refs now runs unconditionally during ingestion. The project argument to TrackOccurrenceRefsEsService existed only as the flag actor, so it is removed as well.

References

• Closes: #613391 (closed)
• Relates to: #605831 (closed)

Screenshots or screen recordings

Flag has been enabled globally

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Related to #605831 (closed)