Clears the current context figure of all marks axes and grid lines.

def clear():
    """Clears the current context figure of all marks axes and grid lines."""
    fig = _context['figure']
    if fig is not None:
        fig.marks = []
        fig.axes = []
        setattr(fig, 'axis_registry', {})
        _context['scales'] = {}
        key = _context['current_key']
        if key is not None:
            _context['scale_registry'][key] = {}