Remove unused code for vulnerability chart on pipeline security tab

What does this MR do?

On the pipeline details page, the security tab shows a list of vulnerabilities:

This MR removes a large swath of code for a vulnerability chart that's no longer used.

For some background, the vulnerability list is a shared component that's used in 4 separate places. Over the past year, we've been converting the vulnerability list from a Vuex implementation to one that uses GraphQL. The GraphQL version was written alongside the Vuex version so that we can switch things over piece by piece.

Currently, there's only one place remaining that still uses the Vuex implementation: the vulnerability list on the pipeline security tab. It has a bunch of code to show a vulnerability chart:

but this is not used on the pipeline security tab and will never be used because we will eventually replace it with the GraphQL version.

Does this MR meet the acceptance criteria?

Conformity

• [-] 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