### What changes were proposed in this pull request?
Update the document and shell script to warn user about the deprecation of multiple workers on the same host support.
### Why are the changes needed?
This is a sub-task of [SPARK-30978](https://issues.apache.org/jira/browse/SPARK-30978), which plans to totally remove support of multiple workers in Spark 3.1. This PR makes the first step to deprecate it firstly in Spark 3.0.
### Does this PR introduce any user-facing change?
Yeah, user see warning when they run start worker script.
### How was this patch tested?
Tested manually.
Closes#27768 from Ngone51/deprecate_spark_worker_instances.
Authored-by: yi.wu <yi.wu@databricks.com>
Signed-off-by: Xingbo Jiang <xingbo.jiang@databricks.com>