Adapt test

disk/src/merge.rs

@@ -1,4 +1,3 @@
-use crate::HasSeenBeforeRangeCount;
 use err::Error;
 use futures_core::Stream;
 use futures_util::StreamExt;
@@ -272,17 +271,6 @@ where
     }
 }
 
-impl<S, ITY> HasSeenBeforeRangeCount for MergedStream<S, ITY>
-where
-    S: Stream<Item = Sitemty<ITY>> + Unpin,
-    ITY: Unpin,
-{
-    fn seen_before_range_count(&self) -> usize {
-        // TODO (only for debug)
-        0
-    }
-}
-
 #[cfg(test)]
 mod test {
     use crate::dataopen::position_file_for_test;