* Removed Scala producers, request classes, kafka.tools.ProducerPerformance, encoders,
tests.
* Updated ConsoleProducer to remove Scala producer support (removed `BaseProducer`
and several options that are not used by the Java producer).
* Updated a few Scala consumer tests to use the new producer (including a minor
refactor of `produceMessages` methods in `TestUtils`).
* Updated `ClientUtils.fetchTopicMetadata` to use `SimpleConsumer` instead of
`SyncProducer`.
* Removed `TestKafkaAppender` as it looks useless and it defined an `Encoder`.
* Minor import clean-ups
No new tests added since behaviour should remain the same after these changes.
Author: Ismael Juma <ismael@juma.me.uk>
Reviewers: Manikumar Reddy O <manikumar.reddy@gmail.com>, Dong Lin <lindong28@gmail.com>
Closes#5045 from ijuma/kafka-6921-remove-old-producer