Refactor e2e specs where possible

[rjimenezda]

With stencil 1 we get a nice new tool that runs components in a puppeteerless environment. In some cases it might be useful using the e2e they provide with a real browser, but for basic snapshot testing the other one is fine, and way faster.

We should at least move all the legend specs to that pattern, check the Stencil 1 PR to see how we refactor some of them