chore: cleanup build warnings

[dan-da]

Hi! I'm not sure if you are ready to accept PRs or not, but this is just a simple cleanup of some build warnings that hopefully you will find an improvement. I'm glad to see openbazaar development resume, and in rust no less! :+1:

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This fixes the trivial build warnings.

note: I removed use statements that are unused, but I left commented anything that I found referenced in commented code below.

A couple of dead-code warnings remain, which seem useful as build-time warnings so they get resolved. So I did not #[allow(dead_code)].