Avoid "ignored-qualifiers" warning in rdkafka.h.

[Romain-Geissler-1A]

This avoid this simple warning:

/remote/tmp/rnd-css/bms_workflow_replica/osp/Librdkafka/23-0-0-4/include/librdkafka/rdkafka.h:8258:1: error: type qualifiers ignored on function return type [-Werror=ignored-qualifiers]
 8258 | const int rd_kafka_TopicPartitionInfo_partition(
      | ^~~~~

indeed returning a const int makes no sense, it's just int.

[confluent-cla-assistant]

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✅ Romain-Geissler-1A
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