Revert "add index accessor for index writer (#1159)"

This reverts commit b256df6599.

src/indexer/index_writer.rs

@@ -348,13 +348,6 @@ impl IndexWriter {
         self.operation_sender = sender;
     }
 
-    /// Accessor to the index
-    ///
-    /// The index is actually cloned.
-    pub fn index(&self) -> &Index {
-        &self.index
-    }
-
     /// If there are some merging threads, blocks until they all finish their work and
     /// then drop the `IndexWriter`.
     pub fn wait_merging_threads(mut self) -> crate::Result<()> {