Remove cluster image scanning dropdown item from scanner filter

What does this MR do and why?

On the vulnerability report, there is a Tools filter dropdown with a number of dropdown items. One of the dropdown items is Cluster Image Scanning. Recently we added an Operational vulnerabilities tab which only shows cluster image scanning results, so we should no longer show the Cluster Image Scanning dropdown item for the Tools filter. This MR removes the dropdown.

Before	After

How to set up and validate locally

1. Set up GitLab Runner to run with a Docker executor. The Docker executor is required because the security scanners use Docker containers.

2. Clone this project locally: https://gitlab.com/gitlab-examples/security/security-reports

3. Run a pipeline against the master branch and verify that it succeeds.

4. Click on Security & Compliance -> Vulnerability report and verify that the vulnerability list has items.

5. Click on the Operational vulnerabilities tab and verify that there are 2 vulnerabilities. There must be at least 1 operational vulnerability in order to verify the bug (and the fix).

6. Click on the Development vulnerabilities tab, then open the Tools filter dropdown. Verify that the Cluster Image Scanning dropdown item is not shown.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #349749 (closed)