Remove Vulnerability-Check

Proposal

All code related to Vulnerability-Check will be removed from the product.

1. Documentation about Vulnerability-Check
   1. https://docs.gitlab.com/ee/user/application_security/#vulnerability-check-rule should be replaced with a reference to scan result policies
   2. The deprecation notice at https://docs.gitlab.com/ee/api/merge_request_approvals.html#create-project-level-rule
   3. The deprecation notice at https://docs.gitlab.com/ee/api/merge_request_approvals.html#update-project-level-rule
2. APIs related to Vulnerability-Check
   1. Note: I do not believe there is any work to do here, but it would be good to double check. The most likely place is in the accepted values for [ApprovalRule.sourceRule](https://docs.gitlab.com/ee/api/graphql/reference/#approvalrule) and [ApprovalRule.type](https://docs.gitlab.com/ee/api/graphql/reference/#approvalrule)
3. Frontend code related to Vulnerability-Check in the Settings > General > Merge Request Approvals page
4. Frontend code related to Vulnerability-Check in the MR page
5. All backend code related to Vulnerability-Check