Retina plots should not render larger than non-retina plots

[timmolendijk]

I ran into #3606, which was diagnosed as a wrapping issue.

But the actual issue reported there is that plots rendered with figure_format = "retina" should not render larger than the default figure_format plots to begin with. This is unresolved as of today and something that is a real problem because it means that I cannot have high-res plots without also having blown-up plots.