[SPARK-37268][SQL] Remove unused method call in FileScanRDD

### What changes were proposed in this pull request?
Remove unused method call in FileScanRDD

### Why are the changes needed?
In PR of SPARK-25674, it directly uses inputMetrics.recordsRead instead of using preNumRecordsRead. So it's necessary to remove unused method call.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

No.

Closes #34545 from zuston/patch-1.

Authored-by: Junfan Zhang <junfan.zhang@outlook.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

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

@@ -107,7 +107,6 @@ class FileScanRDD(
         val nextElement = currentIterator.next()
         // TODO: we should have a better separation of row based and batch based scan, so that we
         // don't need to run this `if` for every record.
-        val preNumRecordsRead = inputMetrics.recordsRead
         if (nextElement.isInstanceOf[ColumnarBatch]) {
           incTaskInputMetricsBytesRead()
           inputMetrics.incRecordsRead(nextElement.asInstanceOf[ColumnarBatch].numRows())