OCPBUGS-65831: Fix catalog service swapping description and markdownDescription fields

[TheRealJon]

The catalog service was incorrectly parsing FBC from catalogd:

• Short plain-text descriptions were stored in markdownDescription
• Long markdown-formatted descriptions were stored in description

This fix corrects the field mapping:

• csvMetadata.Annotations["description"] → item.Description (short, plain-text)
• csvMetadata.Description → item.MarkdownDescription (long, markdown)

Also removed fallback logic for markdownDescription to keep it empty when not available, and removed unused pkg parameter.

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