git-rebase: Update --whitespace documentation

The parameters accepted by the --whitespace option of "git apply" have changed over time, and the documentation for "git rebase" was out of sync. Remove the specific parameter list from the "git rebase" documentation and simply point to the "git apply" documentation for details, as is already done in the "git am" documentation. Signed-off-by: Todd Zullinger <tmz@pobox.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>