[SPARK-45902][SQL] Remove unused function resolvePartitionColumns from DataSource

### What changes were proposed in this pull request?
`resolvePartitionColumns` was introduced by SPARK-37287 (#37099) and become unused after SPARK-41713 (#39220), so this pr remove it from `DataSource`.

### Why are the changes needed?
Clean up unused code.

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

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

### Was this patch authored or co-authored using generative AI tooling?
No

Closes #43779 from LuciferYang/SPARK-45902.

Lead-authored-by: yangjie01 <[email protected]>
Co-authored-by: YangJie <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: LuciferYang

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala

@@ -29,9 +29,8 @@ import org.apache.spark.SparkException
 import org.apache.spark.deploy.SparkHadoopUtil
 import org.apache.spark.internal.Logging
 import org.apache.spark.sql._
-import org.apache.spark.sql.catalyst.analysis.{Resolver, UnresolvedAttribute}
+import org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute
 import org.apache.spark.sql.catalyst.catalog.{BucketSpec, CatalogStorageFormat, CatalogTable, CatalogUtils}
-import org.apache.spark.sql.catalyst.expressions.Attribute
 import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
 import org.apache.spark.sql.catalyst.util.{CaseInsensitiveMap, TypeUtils}
 import org.apache.spark.sql.connector.catalog.TableProvider
@@ -822,26 +821,4 @@ object DataSource extends Logging {
       throw QueryCompilationErrors.writeEmptySchemasUnsupportedByDataSourceError()
     }
   }
-
-  /**
-   * Resolve partition columns using output columns of the query plan.
-   */
-  def resolvePartitionColumns(
-      partitionColumns: Seq[Attribute],
-      outputColumns: Seq[Attribute],
-      plan: LogicalPlan,
-      resolver: Resolver): Seq[Attribute] = {
-    partitionColumns.map { col =>
-      // The partition columns created in `planForWritingFileFormat` should always be
-      // `UnresolvedAttribute` with a single name part.
-      assert(col.isInstanceOf[UnresolvedAttribute])
-      val unresolved = col.asInstanceOf[UnresolvedAttribute]
-      assert(unresolved.nameParts.length == 1)
-      val name = unresolved.nameParts.head
-      outputColumns.find(a => resolver(a.name, name)).getOrElse {
-        throw QueryCompilationErrors.cannotResolveAttributeError(
-          name, plan.output.map(_.name).mkString(", "))
-      }
-    }
-  }
 }