Remove unused refetch vulnerabilities code

What does this MR do?

On the security dashboard, you can bulk dismiss vulnerabilities:

Currently, the code tries to refetch vulnerabilities after the bulk dismiss is finished in order to update the vulnerabilities. However, Apollo is smart enough to update its in-memory cache from the dismissal mutation, and also smart enough to not perform a network request despite the call to refetch():

This MR simply removes the code that attempts this, since it doesn't do anything anyway, and removing it preserves the same behavior.

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