compose: Disable yumdb by default

This API was added to libhif a while ago.  I'm adding this now because
libhif was changed recently to write the dnf copy of the yumdb, and we
didn't have code to remove it explicitly.

It's better not to write it in the first place.

src/app/rpmostree-compose-builtin-tree.c

@@ -211,6 +211,8 @@ install_packages_in_root (RpmOstreeTreeComposeContext  *self,
   hif_context_set_check_disk_space (hifctx, FALSE);
   hif_context_set_check_transaction (hifctx, FALSE);
 
+  hif_context_set_yumdb_enabled (hifctx, FALSE);
+
   hif_context_set_repo_dir (hifctx, gs_file_get_path_cached (contextdir));
 
   { JsonNode *install_langs_n =