Remove references to deprecated python environment variables

[sarah-witt]

What does this PR do?

Remove references to DD_AGENT_PY and DD_AGENT_PY_ENV as known env vars included in the flare. These two variables are not used in the agent or process agent anymore since agent 6.11.0.

Motivation

They were added in DataDog/datadog-process-agent#50 and removed in DataDog/datadog-process-agent#272

We used to use them in the bosh release but now they are not used in the agent at all.

Additional Notes

companion to DataDog/datadog-agent-boshrelease#178

Possible Drawbacks / Trade-offs

Describe how to test/QA your changes

Reviewer's Checklist

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• If applicable, the config template has been updated.