If scheduled messages are excluded due to last min bookings, don't generate them

In the case that Exclude last minute bookings is enabled on a messaging rule, the message should not be generated at all. The message is currently generated and then canceled, but no information is given in the UI to indicate why it was canceled. This leads to confusion for the host. Ideally, if a reservation is excluded from a messaging rule, we shouldn't be generating the message in the first place. Alternatively, provide more information in the UI as to why the message has been canceled.