Remove unused infinite retry code from ActiveContext

Description

Follow-up to !251318 (merged). Since the retry chain, nothing passes infinite_retry_error_types: rate-limited batches walk the chain like every other failure. This removes the dead code: the kwarg and its rescue branch, the retryable result bucket, and the retryable_count and infinite_retry log fields. No behavior change.

Related to #606544 (closed).