In commit 735285b403 ("am: fix signoff when other trailers are present",
2017-08-08) tests using variable $signoff were rewritten and it is no
longer used, so just remove it from the test setup.
Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>