seg: make prune run as an rotx reader (#12396)

Try closing and removing canDelete files only when closing rotx. 

reason: `merge` and `prune`, running as rotx reader, will increase
`refCount`

turbo/snapshotsync/merger.go

@@ -236,9 +236,6 @@ func (m *Merger) integrateMergedDirtyFiles(snapshots *RoSnapshots, in, out map[s
 		for _, delSeg := range delSegs {
 			dirtySegments.Delete(delSeg)
 			delSeg.canDelete.Store(true)
-			if delSeg.refcount.Load() == 0 {
-				delSeg.closeAndRemoveFiles()
-			}
 		}
 	}
 }

turbo/snapshotsync/snapshots.go

@@ -1291,9 +1291,6 @@ func (s *RoSnapshots) delete(fileName string) error {
 					continue
 				}
 				sn.canDelete.Store(true)
-				if sn.refcount.Load() == 0 {
-					sn.closeAndRemoveFiles()
-				}
 				delSeg = sn
 				dirtySegments = s.dirty[t]
 				findDelSeg = false
@@ -1314,6 +1311,10 @@ func (s *RoSnapshots) Delete(fileName string) error {
 	if s == nil {
 		return nil
 	}
+
+	v := s.View()
+	defer v.Close()
+
 	defer s.recalcVisibleFiles()
 	if err := s.delete(fileName); err != nil {
 		return fmt.Errorf("can't delete file: %w", err)