deltas: Make ostree_repo_static_delta_reindex() public

It is useful to be able to trigger this without having to regenerate
the summary. For example, if you are not using summaries, or ar generating
the summaries yourself.

src/libostree/ostree-repo.c

@@ -5935,7 +5935,7 @@ ostree_repo_regenerate_summary (OstreeRepo     *self,
     g_variant_ref_sink (summary);
   }
 
-  if (!_ostree_repo_static_delta_reindex (self, NULL, cancellable, error))
+  if (!ostree_repo_static_delta_reindex (self, 0, NULL, cancellable, error))
     return FALSE;
 
   if (!_ostree_repo_file_replace_contents (self,