Resolve "Deleting a booking by the guest shouldn't trigger a mail"

What does this MR do?

If a guest removes a booking, he/she shouldn't get a mail about it. It was likely a concious decision.

Closes #266 (closed)

Does this MR meet the acceptance criteria?

• I have added tests to validate the fix.
• I have updated the documentation accordingly.
• I have added translations for all new client-side text.
• I have updated the changelog accordingly.