Add stash pop to the helper and delete the pop_stash, drop_stash,
assert_stash_ref functions from the shell script now that they
are no longer needed.
Signed-off-by: Joel Teichroeb <joel@teichroeb.net> Signed-off-by: Paul-Sebastian Ungureanu <ungureanupaulsebastian@gmail.com> Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>