Fix revision height used for trusted validator set queries

[colin-axner]

Summary

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The testing pkg should use the trusted height (without a + 1) to query for the trusted validator set through historical information. The API should be updated as well to clarify this interaction/expectations.

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[damiannolan]

Can we close this issue now @colin-axner? Or did you want to keep it open for further follow ups?

[colin-axner]

I was thinking of leaving this open until this API is updated or deleted, #4483 (comment) (addressing post v8 release)