CamelSinkTask headers must be cleaned before sending them ahead

[oscerd]

https://github.com/apache/camel-kafka-connector/blob/master/core/src/main/java/org/apache/camel/kafkaconnector/CamelSinkTask.java#L117

Actually we are sending the header with the prefix set for distinguishing between camel headers and kafka headers, but we need to remove the prefix before going ahead.