[aztables] Remove odd env variables stored in eng/config.json

[richardpark-msft]

(This came up in #23596)

There are some hardcoded variables for the CosmoDB emulator that are stored in eng/config.json that get injected into the CI pipeline. Injecting these via config.json is a technique that nobody uses, so it confused everyone and (since it's a JSON file without comments) it's not obvious what those values are for.

It'd be better to move them locally, into the test, rather than having them be stored for both data and now, data/aztables.