Removes a callback.

def remove(self, cb):
        """Removes a callback."""
        if cb in self.callbacks:
            self.callbacks.remove(cb)
            new_monitor = 0
            for c in self.callbacks:
                new_monitor |= c.bit
            if new_monitor != self.monitor:
                self.monitor = new_monitor
                yield from self.pi._pigpio_aio_command(
                    _PI_CMD_NB, self.handle, self.monitor)