Updates delete icon button in runner table

What does this MR do and why?

Update delete icon button in runner table to use secondary variant.

From #360430 (closed):

When looking at the runner table in the admin area today, the delete button sticks out the most since it is using a primary variant. We've updated that to use the secondary variant to draw attention towards the important data on the page instead and to be consistent with the runner details page.

This MR resolves this issue.

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