core: Make ostree_get_relative_object_path() private

I plan to rename all of these APIs to use the term 'loose', so that it
makes more sense after pack files are introduced.  External users
should not use them; instead use _load_variant() or _read_commit().

src/libostree/ostree-core.c

@@ -1497,8 +1497,8 @@ _ostree_loose_path_with_suffix (char              *buf,
             suffix);
 }
 
-/**
- * ostree_get_relative_object_path:
+/*
+ * _ostree_get_relative_object_path:
  * @checksum: ASCII checksum string
  * @type: Object type
  * @compressed: Whether or not the repository object is compressed
@@ -1506,9 +1506,9 @@ _ostree_loose_path_with_suffix (char              *buf,
  * Returns: (transfer full): Relative path for a loose object
  */
 char *
-ostree_get_relative_object_path (const char         *checksum,
-                                 OstreeObjectType    type,
-                                 gboolean            compressed)
+_ostree_get_relative_object_path (const char         *checksum,
+                                  OstreeObjectType    type,
+                                  gboolean            compressed)
 {
   GString *path;