Remove threat monitoring statistics tab Vuex

What does this MR do and why?

Remove threat monitoring statistics tab Vuex

• remove vuex and tests, which are no longer used after Remove threat monitoring sidebar option and routes (!82315 - merged) was merged
• the threat monitoring paths have already been removed, so none of these are used
• components are removed in !85651 (merged)

Related to #352287 (closed)

What does this MR NOT do and why?

It doesn't remove any of the Vue components because that would push this MR to be even larger than it is (see Draft: Remove threat monitoring statistics tab (!82132 - closed)), so that is coming in a follow-up MR

It doesn't even remove ALL of the components because that would push this MR to be even larger. Everything will be deleted in time

Screenshots or screen recordings

These components were no longer used after Remove threat monitoring sidebar option and routes (!82315 - merged), so this will not break anything

How to set up and validate locally

N/A

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.