Update Kafka tutorial to work with Apache Kafka (tensorflow#1266)

* Update Kafka tutorial to work with Apache Kafka

Minor update to the Kafka tutorial to remove the dependency on
Confluent's distribution of Kafka, and instead work with vanilla
Apache Kafka.

Signed-off-by: Dale Lane <dale.lane@uk.ibm.com>

* Address review comments

Remove redundant pip install commands

Signed-off-by: Dale Lane <dale.lane@gmail.com>

Author: dalelane

docs/tutorials/kafka.ipynb

@@ -74,7 +74,7 @@
         "\n",
         "Kafka is primarily a distributed event-streaming platform which provides scalable and fault-tolerant streaming data across data pipelines. It is an essential technical component of a plethora of major enterprises where mission-critical data delivery is a primary requirement.\n",
         "\n",
-        "**NOTE:** A basic understanding of the [kafka components](https://kafka.apache.org/documentation/#intro_concepts_and_terms) will help you in following the tutorial with ease.\n",
+        "**NOTE:** A basic understanding of the [kafka components](https://kafka.apache.org/documentation/#intro_concepts_and_terms) will help you in following the tutorial with ease.",
         "\n",
         "**NOTE:** A Java runtime environment is required to run this tutorial."
       ]