Update how-to-oracles

[Savio-Sou]

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1. feat!: separate proving from noir_js noir-lang/noir#5072
   documentation +1

Following noir-lang/noir#5072, proving and verification workflow would no longer rely on NoirJS but proving backends' JS packages (e.g. bb.js) instead.

That in turn requires updating the instructions of how JS packages are used in the https://noir-lang.org/docs/how_to/how-to-oracles doc page.

As the how-to-oracles example in this repo is linked and used as the basis of that doc page, we would have to update it as a part of updating the doc page.