[SPARK-44607][SQL] Remove unused function containsNestedColumn from…

… `Filter`

### What changes were proposed in this pull request?
This pr aims remove `private[sql] `function `containsNestedColumn` from `org.apache.spark.sql.sources.Filter`.
This function was introduced by #27728 to avoid nested predicate pushdown for Orc.
After #28761, Orc also support nested column predicate pushdown, so this function become unused.

### Why are the changes needed?
Remove unused `private[sql] ` function `containsNestedColumn`.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
Pass GitHub Actions

Closes #42239 from LuciferYang/SPARK-44607.

Authored-by: yangjie01 <[email protected]>
Signed-off-by: yangjie01 <[email protected]>

sql/catalyst/src/main/scala/org/apache/spark/sql/sources/filters.scala

@@ -64,13 +64,6 @@ sealed abstract class Filter {
     this.references.map(parseColumnPath(_).toArray)
   }
 
-  /**
-   * If any of the references of this filter contains nested column
-   */
-  private[sql] def containsNestedColumn: Boolean = {
-    this.v2references.exists(_.length > 1)
-  }
-
   /**
    * Converts V1 filter to V2 filter
    */