[ML][MINOR] Make sharedParams update.

## What changes were proposed in this pull request?
```sharedParams.scala``` was generated by ```SharedParamsCodeGen```, but it's not updated in master. Maybe someone manual update ```sharedParams.scala```, this PR fix this issue.

## How was this patch tested?
Offline check.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #19011 from yanboliang/sharedParams.

mllib/src/main/scala/org/apache/spark/ml/param/shared/sharedParams.scala

@@ -154,7 +154,7 @@ private[ml] trait HasVarianceCol extends Params {
 }
 
 /**
- * Trait for shared param threshold (default: 0.5).
+ * Trait for shared param threshold.
  */
 private[ml] trait HasThreshold extends Params {