Resolve CCL License headers in client libraries

[elahrvivaz]

Hello,

The following files still have CCL licenses, while both the poms and LICENSE files indicate Apache 2. I saw previously some licenses were incorrect and fixed (i.e. #2073), could the same be done here?

kafka-schema-registry-client:

• io.confluent.kafka.schemaregistry.avro.Difference
• io.confluent.kafka.schemaregistry.client.rest.entities.SchemaRegistryServerVersion

kafka-schema-serializer:

• io.confluent.kafka.serializers.WrapperKeyDeserializer
• io.confluent.kafka.serializers.WrapperKeyDeserializerConfig
• io.confluent.kafka.serializers.WrapperKeySerializer
• io.confluent.kafka.serializers.WrapperKeySerializerConfig

Thanks,