V0Tools: Remove extrapolator and simplify

Closed Adam Edward Barton requested to merge abarton/athena:V0Clean into master

No code actually uses the extrapolator in V0Tools. So here I factor it out. This simplifies configuration of tools. Any algorithm wanting to use those functions can pass an extrapolator.

I also remove some unused convenience functions that make maintenance harder. Once we have C++20 I will add spans to simplify things further.

Request opinions from @christos @tstreble @bouhova

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