store: Drop pub for internal composefs ref

This was a copy-pasteo from the ostree bits.

Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

crates/lib/src/store/mod.rs

@@ -58,7 +58,7 @@ pub(crate) struct Storage {
     /// The OSTree storage
     ostree: SysrootLock,
     /// The composefs storage
-    pub composefs: OnceCell<Arc<ComposefsRepository>>,
+    composefs: OnceCell<Arc<ComposefsRepository>>,
     /// The containers-image storage used foR LBIs
     imgstore: OnceCell<crate::imgstorage::Storage>,