Tell Secure reports are no longer fetched by frontend (code comment)

What does this MR do?

Update code comment in the Rails backend to indicate that security reports and license scanning are no longer fetched by the frontend, though that used to be the case.

This MR does NOT change the code itself.

See discussion in #235390 (comment 424818698)

Screenshots

N/A

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• [-] Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

N/A

Security

N/A