[VULN-649] ci: Remove deprecated scan workflow

[theMickster]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/VULN-649

📔 Objective

Removes the deprecated scan.yml GitHub Actions workflow.

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: APPROVE

This PR removes the deprecated scan.yml GitHub Actions workflow (Checkmarx SAST and Sonar quality jobs) under VULN-649. The scanning functionality is preserved in scan-ci.yml, which runs the same Checkmarx and Sonar jobs on push to main. No remaining references to the deleted workflow exist in the repository, so this is a clean removal with no orphaned configuration.

Code Review Details

No findings. The change is a straightforward deletion of a superseded CI workflow:

• The deleted scan.yml triggered on pull requests; the surviving scan-ci.yml runs the equivalent Checkmarx/Sonar jobs on push to main.
• A repository-wide search found no other references to scan.yml or the "Scan Pull Requests" workflow name (branch protection, docs, or other workflows).
• Change is tracked under VULN-649 and labeled t:ci, consistent with an intentional CI process decision.