commit-reach: reduce requirements for remove_redundant()

commit-reach: reduce requirements for remove_redundant()

Remove a comment at the beggining of remove_redundant() that mentions a
reordering of the input array to have the initial segment be the
independent commits and the final segment be the redundant commits.
While this behavior is followed in remove_redundant(), no callers rely
on that behavior.

Remove the final loop that copies this final segment and update the
comment to match the new behavior.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>