Don't invoke the service in `confest.py` fixtures

[data-sync-user]

The integration tests' confest.py invokes the rust service for the tests to run against. It supports invoking with an optional JWK_CACHE_DISABLED env var (which invokes the service without setup of various JWK config vars).

This is a leftover of the original, non py.test based test runner which also needed to support other configurations (running against oauth vs browserid).

Invoking the service here was never ideal for a not uncommon case of local development without using docker: you should be able to run the service locally and invoke the integration tests with py.test, pointing to your local instance, without fixtures attempting to invoke its own version of the service.

We also invoke the integration tests via docker compose, which invokes its own instance of the service. When they run they’re actually running two versions of the service

We should make docker compose responsible for invoking the service the integration tests run against. Maybe we can have some cleverness with environment variables where we can run the compose setup in different modes, e.g. docker compose -e JWK_CACHE_DISABLED=true

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