[KYUUBI #5957] Flink engine should not load kyuubi-defaults.conf

# 🔍 Description

This is the root cause of #5957. Which is accidentally introduced in b315123a6b, thus affects 1.8.0, 1.8.1， 1.8.2, 1.9.0, 1.9.1.

`kyuubi-defaults.conf` is kind of a server side configuration file, all Kyuubi confs engine required should be passed via CLI args to sub-process.

## Types of changes 🔖

- [x] Bugfix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

## Test Plan 🧪

Pass GHA.

---

# Checklist 📝

- [x] This patch was not authored or co-authored using [Generative Tooling](https://www.apache.org/legal/generative-tooling.html)

**Be nice. Be informative.**

Closes #6455 from pan3793/flink-conf-load.

Closes #5957

2972fbc98 [Cheng Pan] Flink engine should not load kyuubi-defaults.conf

Authored-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: Cheng Pan <chengpan@apache.org>
(cherry picked from commit fe5377e0fa)
Signed-off-by: Cheng Pan <chengpan@apache.org>

externals/kyuubi-flink-sql-engine/src/main/scala/org/apache/kyuubi/engine/flink/FlinkSQLEngine.scala

@@ -75,7 +75,6 @@ object FlinkSQLEngine extends Logging {
     FlinkEngineUtils.checkFlinkVersion()
 
     try {
-      kyuubiConf.loadFileDefaults()
       Utils.fromCommandLineArgs(args, kyuubiConf)
       val flinkConfDir = sys.env.getOrElse(
         "FLINK_CONF_DIR", {