## What changes were proposed in this pull request?

Currently, `spark.executor.instances` is deprecated in `spark-env.sh`, because we suggest config it in `spark-defaults.conf` or other config file. And also this parameter is useless even if you set it in `spark-env.sh`, so remove it in this patch.

## How was this patch tested?

Existing tests.

Please review http://spark.apache.org/contributing.html before opening a pull request.

Author: Xianyang Liu <xianyang.liu@intel.com>

Closes #17881 from ConeyLiu/deprecatedParam.