test: refactor EvalEndpoint_Delete (#15065)
test: refactor EvalEndpoint_Delete (#15065)

While working on filtering improvements to the `Eval.Delete` endpoint I noticed
that this test was going to need to expand significantly and needed some
refactoring to make that work nicely. In order to reduce the size of the
eventual diff, I've pulled this refactoring out into its own changeset.
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