Remove @types/plotly.js dependency #5740

@types/plotly.js (the DefinitelyTyped types for plotly.js) is listed as a dev dependency in js/package.json.

As of plotly.js 4.0.0, types are included in plotly.js itself (see plotly/plotly.js#7680), so we can probably remove the @types/plotly.js dependency. I haven't looked into how the types are actually used in the code.