The appointment receipt format can be simplified (appointment_accepted)

[sr-gi]

The current signature format for an appointment_accepted message is:

locator | encrypted_blob | to_self_delay | user_signature | start_block

However, the user_signature field already covers the first three fields. Therefore, the receipt could be simplified to:

user_signature | start_block

On disputes, the tower can prove that an appointment was requested by showing the appointment data (that is kept until completion) and the user signature, whereas the user can prove the tower agreement by showing the receipt signature.