reset.c: remove unnecessary variable 'i'

reset.c: remove unnecessary variable 'i'

Throughout most of parse_args(), the variable 'i' remains at 0. Many
references are still made to the variable even when it could only have
the value 0. This made at least me, who has relatively little
experience with C programming styles, think that parts of the function
was meant to be part of a loop. To avoid such confusion, remove the
variable and also the 'argc' parameter and check for NULL trailing
argv instead.

Signed-off-by: Martin von Zweigbergk <martinvonz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>