index: make ReadonlyIndexImpl private

There are no external callers.

lib/src/default_index_store.rs

@@ -370,7 +370,7 @@ pub enum IndexLoadError {
 // TODO: replace the table by a trie so we don't have to repeat the full commit
 //       ids
 // TODO: add a fanout table like git's commit graph has?
-pub(crate) struct ReadonlyIndexImpl {
+struct ReadonlyIndexImpl {
     parent_file: Option<Arc<ReadonlyIndexImpl>>,
     num_parent_commits: u32,
     name: String,
@@ -447,7 +447,7 @@ impl MutableIndexImpl {
         }
     }
 
-    pub(crate) fn incremental(parent_file: Arc<ReadonlyIndexImpl>) -> Self {
+    fn incremental(parent_file: Arc<ReadonlyIndexImpl>) -> Self {
         let num_parent_commits = parent_file.num_parent_commits + parent_file.num_local_commits;
         let commit_id_length = parent_file.commit_id_length;
         let change_id_length = parent_file.change_id_length;
@@ -1877,7 +1877,7 @@ impl ReadonlyIndexImpl {
         }))
     }
 
-    pub fn as_composite(&self) -> CompositeIndex {
+    fn as_composite(&self) -> CompositeIndex {
         CompositeIndex(self)
     }