worktree: drop get_worktrees() special-purpose sorting option

worktree: drop get_worktrees() special-purpose sorting option

Of all the clients of get_worktrees(), only "git worktree list" wants
the list sorted in a very specific way; other clients simply don't care
about the order. Rather than imbuing get_worktrees() with special
knowledge about how various clients -- now and in the future -- may want
the list sorted, drop the sorting capability altogether and make it the
client's responsibility to sort the list if needed.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>