KAFKA-9922: Update demo instructions in examples README (#8559)

Class kafka.examples.SimpleConsumerDemo was removed. But the java-simple-consumer-demo.sh was not removed and README was not updated.

This commit removes java-simple-consumer-demo.sh and updates the demo instructions in the examples README. 

Author: Jiamei Xie <jiamei.xie@arm.com>
Reviewers: Konstantine Karantasis <konstantine@confluent.io>

examples/README

@@ -1,13 +1,12 @@
 This directory contains examples of client code that uses kafka.
 
-To run the demo: 
+To run the demo:
 
    1. Start Zookeeper and the Kafka server
-   2. For simple consumer demo, `run bin/java-simple-consumer-demo.sh`
+   2. For unlimited sync-producer-consumer run, `run bin/java-producer-consumer-demo.sh sync`
-   3. For unlimited sync-producer-consumer run, `run bin/java-producer-consumer-demo.sh sync`
+   3. For unlimited async-producer-consumer run, `run bin/java-producer-consumer-demo.sh`
-   4. For unlimited async-producer-consumer run, `run bin/java-producer-consumer-demo.sh`
+   4. For exactly once demo run, `run bin/exactly-once-demo.sh 6 3 50000`,
-   5. For exactly once demo run, `run bin/exactly-once-demo.sh 6 3 50000`,
       this means we are starting 3 EOS instances with 6 topic partitions and 50000 pre-populated records.
-   6. Some notes for exactly once demo:
+   5. Some notes for exactly once demo:
-      6.1. The Kafka server has to be on broker version 2.5 or higher.
+      5.1. The Kafka server has to be on broker version 2.5 or higher.
-      6.2. You could also use Intellij to run the example directly by configuring parameters as "Program arguments"
+      5.2. You could also use Intellij to run the example directly by configuring parameters as "Program arguments"

examples/bin/java-simple-consumer-demo.sh

@@ -1,22 +0,0 @@
-#!/bin/bash
-# Licensed to the Apache Software Foundation (ASF) under one or more
-# contributor license agreements.  See the NOTICE file distributed with
-# this work for additional information regarding copyright ownership.
-# The ASF licenses this file to You under the Apache License, Version 2.0
-# (the "License"); you may not use this file except in compliance with
-# the License.  You may obtain a copy of the License at
-# 
-#    http://www.apache.org/licenses/LICENSE-2.0
-# 
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-base_dir=$(dirname $0)/../..
-
-if [ "x$KAFKA_HEAP_OPTS" = "x" ]; then
-    export KAFKA_HEAP_OPTS="-Xmx512M"
-fi
-exec $base_dir/bin/kafka-run-class.sh kafka.examples.SimpleConsumerDemo $@