Remove security_on_demand_scans_scanner_profiles feature flag

• Related issue: #235545 (closed)

What does this MR do?

Removes the security_on_demand_scans_scanner_profiles feature flag and all associated logic

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry (not needed as the feature flag was enabled by default in !41950 (merged), which included a changelog entry)
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done