Add warning about Expires; remove green box

[joker314]

I'm not sure if zero, one or both of these changes are needed (please comment)

• The green box saying that the form is up to date is now redundant, because no further changes are likely to be made to the draft (so we can essentially guarantee the form is up-to-date). Hence, the green box is removed.
• An orange box is added to warn that the date format for Expires has recently changed.

Old:

New: