Fix remove approver prompt cancel

What does this MR do?

Fix issue of approver still being removed even when 'cancel' is clicked (video).
Use confirm:complete event to examine confirm dialog result.

What are the relevant issue numbers?

Fix #6760 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• EE specific content should be in the top level /ee folder

Closes #6760 (closed)