ref(rust): Remove unused CLI option max_bytes_before_external_group_by

[untitaker]

depends on successful rollout of https://github.com/getsentry/ops/pull/13279

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: snuba/cli/rust_consumer.py

Function	Unhandled Issue
rust_consumer	PanicException: called Result::unwrap() on an Err value: KafkaError (Consumer commit error: BrokerDestroy (Lo... ... Event Count: 3

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