shelve: remove unused variable assignment Fix test-check-pyflakes.t error after 1d7a36ff2615. This patch replaces "readshelvedfiles()" invocation by "shelvedfile().exists()" check and aborting, because it is required only to ensure that shelved changes corresponded to specified name exist after invocation. This patch also remove definition of "readshelvedfiles()" itself, because it is invoked only from the line removed by this patch.