Revert "Update last_activity when not using sendfile as well"

This reverts commit b2c4c9422e.

last_activity is already updated in the send() method

src/calibre/srv/http_response.py

@@ -343,7 +343,6 @@ class HTTPConnection(HTTPRequest):
                 raise IOError('sendfile() failed to write any bytes to the socket')
         else:
             sent = self.send(buf.read(min(limit, self.send_bufsize)))
-            self.last_activity = monotonic()
         buf.seek(pos + sent)
         return buf.tell() == end