Strip replies when calling EventHandler::getMarkdownBody()

This matches previous behavior before
e2eb6ab33c and including the markdown
blockquote breaks edits. This also adds a test to ensure it does indeed
get stripped.

src/eventhandler.cpp

@@ -293,7 +293,10 @@ QString EventHandler::getMarkdownBody() const
     }
 
     const auto roomMessageEvent = eventCast<const RoomMessageEvent>(m_event);
-    return roomMessageEvent->plainBody();
+
+    QString plainBody = roomMessageEvent->plainBody();
+    plainBody.remove(TextRegex::removeReply);
+    return plainBody;
 }
 
 QString EventHandler::getBody(const Quotient::RoomEvent *event, Qt::TextFormat format, bool stripNewlines) const