Simplify route caching lookup

What does this MR do?

Fix for the work in !57027 (merged). Turns out the preload-detection stuff can't possibly work due to the way in which the route relationship is configured - we can't do route.present? without performing the query we're trying to avoid. So this MR removes all the code around that and just goes straight to the cached form.

Related #325334 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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