Remove the quote-style around message in notification emails

Rationale:

* In this notification email, the message is the most important content.
It should not be dimmed or smaller than the rest of the text.

* Now that all UI elements are removed, the message *is* the email. It
should be written as a standard email message, without styling.

app/views/notify/_note_message.html.haml

-%cite{style: 'color: #666'}
+%div
   = markdown(@note.note)