chore(ppf): Stop sending group states from the post process forwarder

[wedamija]

We stop relying on group_states in #63130. Once this has merged and is in production, we can stop sending group_states entirely via the ppf.

We can stop including the group_states info in the Kafka messages in a later pr

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
23900	1	23899	292

View the top 1 failed test(s) by shortest run time

tests.sentry.eventstream.kafka.test_protocol::test_get_task_kwargs_for_message_version_1

Stack Traces | 0.055s run time

#x1B[1m#x1B[.../eventstream/kafka/test_protocol.py#x1B[0m:62: in test_get_task_kwargs_for_message_version_1
    assert kwargs.pop("group_states") is None
#x1B[1m#x1B[31mE   KeyError: 'group_states'#x1B[0m

To view more test analytics, go to the Test Analytics Dashboard
_{📋 Got 3 mins? Take this short survey to help us improve Test Analytics.}

[JoshFerge]

are we still interested in this changeset?

[wedamija]

@JoshFerge yeah, we should clean this up. I haven't had a chance to work on this because it's not urgent, but it'd be nice to have this be a little cleaner and remove unused junk