Revert "Also use 'track_object_refs = 0' in update-server-info."

This reverts d119e3de13ea1493107bd57381d0ce9c9dd90976 commit.

Object references are used in server-info.c:find_pack_info_one() to
find out which objects in the pack are heads, therefore tracking of
references cannot be disabled.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Signed-off-by: Junio C Hamano <junkio@cox.net>