input: kafka: Remove duplicate poll_ms config (fluent#1414)

Signed-off-by: Seonghyeon Cho <[email protected]>

Author: sh-cho

pipeline/inputs/kafka.md

@@ -14,7 +14,6 @@ This plugin uses the official [librdkafka C library](https://github.com/edenhill
 | group\_id | Group id passed to librdkafka. | fluent-bit |
 | poll\_ms | Kafka brokers polling interval in milliseconds. | 500 |
 | Buffer\_Max\_Size | Specify the maximum size of buffer per cycle to poll kafka messages from subscribed topics. To increase throughput, specify larger size. | 4M |
-| poll\_ms | Kafka brokers polling interval in milliseconds. | 500 |
 | rdkafka.{property} | `{property}` can be any [librdkafka properties](https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.md) |  |
 
 ## Getting Started