[3.0.0] Use api-utils for currency definitions

[aldeed]

Resolves #5822
Impact: breaking
Type: feature|bugfix

Issue

Earlier in the 3.0.0 release, we stopped setting shop.currencies because it was the same for every shop. We also removed most of the exchange rates feature because it was poorly implemented. But there were still some places in the code checking shop.currencies.

Solution

Remove remaining use of shop.currencies.

• Update setAccountProfileCurrency gql mutation to use CurrencyDefinitions from api-utils package instead of shop.currencies
• Remove exchange rate handling from placeOrder. It was only half implemented and never tested, and it relied on shop.currencies
• Update publishProductToCatalog mutation function to use CurrencyDefinitions from api-utils package instead of shop.currencies
• Update simple-pricing plugin to no longer include currencyExchangePricing object on prices. This was effectively broken by earlier changes removing exchange rate updating and it relied on shop.currencies

Breaking changes

The currencyExchangePricing field is no longer available on ProductPricingInfo type in GraphQL (simple-pricing plugin)

Testing

Main areas of testing:

• placing an order works
• publishing a product to catalog works

[kieckhafer]

👍 able to perform the actions i wasn't able to before this PR