The function 'add_oid_to_argv()' provides the same functionality as
'append_oid_to_argv()'. Remove this duplicate function and instead use
'append_oid_to_argv()' where 'add_oid_to_argv()' was previously used.
Signed-off-by: Brandon Williams <bmwill@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>