Deleted axes not cleaned up properly

[alexcjohnson]

See eg:

Plotly.newPlot(gd,
 [{y: [1,2,3]}, {y: [10, 30, 20], yaxis: 'y2'}],
 {yaxis2: {side: 'right', overlaying: 'y'}}
);
Plotly.deleteTraces(gd, [1]);

reported in plotly/react-plotly.js#45

[krunomunitic]

Also experiencing this 👍