Fix blockstore-purge delete_files_in_range_us metric (solana-labs#33512)

This field was being filled with the wrong value

ledger/src/blockstore/blockstore_purge.rs

@@ -50,7 +50,7 @@ impl Blockstore {
             ("write_batch_us", purge_stats.write_batch as i64, i64),
             (
                 "delete_files_in_range_us",
-                purge_stats.write_batch as i64,
+                purge_stats.delete_files_in_range as i64,
                 i64
             )
         );