Remove Security Configuration ProjectSetContinuousVulnerabilityScanning

Why are we doing this work

Continuous Vulnerability Scanning is now a default feature and has been enabled as part of an epic. The task at hand involves removing the outdated security configuration setting continuous_vulnerability_scans_enabled, related code and graphql mutation Mutations::Security::CiConfiguration::ProjectSetContinuousVulnerabilityScanning from the GitLab backend.

Non-functional requirements

• Documentation:
• Feature flag:
• Testing: