Since 833622a945 ("stash push: avoid printing errors", 2018-03-19) we
don't use the 'git clean' call for the pathspec case anymore. The
commit however forgot to remove the pathspec argument to the call.
Remove the superfluos argument to make the code a little more obvious.
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>