Internal: remove unused, undocumented AnymailInboundEvent attrs

AnymailInternalEvent had some properties that were actually implemented
in AnymailInboundMessage. The event versions were never documented,
and never contained useful data (they were always set to None).

anymail/signals.py

@@ -46,17 +46,6 @@ class AnymailInboundEvent(AnymailEvent):
     def __init__(self, **kwargs):
         super(AnymailInboundEvent, self).__init__(**kwargs)
         self.message = kwargs.pop('message', None)  # anymail.inbound.AnymailInboundMessage
-        self.recipient = kwargs.pop('recipient', None)  # str: envelope recipient
-        self.sender = kwargs.pop('sender', None)  # str: envelope sender
-
-        self.stripped_text = kwargs.pop('stripped_text', None)  # cleaned of quotes/signatures (varies by ESP)
-        self.stripped_html = kwargs.pop('stripped_html', None)
-        self.spam_detected = kwargs.pop('spam_detected', None)  # bool
-        self.spam_score = kwargs.pop('spam_score', None)  # float: usually SpamAssassin
-
-        # SPF status?
-        # DKIM status?
-        # DMARC status? (no ESP has documented support yet)
 
 
 class EventType: