[Subheader] Remove desktop and focusState props from being passed to <div>

[billyvg]

If you use a <Subheader> inside of a <Menu>, it can be passed these two props which are then passed to a <div>

Fixes #5830

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".
• Description explains the issue / use-case resolved, and auto-closes the related issue(s) (http://tr.im/vFqem).

[oliviertassinari]

I would rather have the Menu passing those properties to a white list of components. I think that we are leaking concerns here.

[billyvg]

@oliviertassinari Should I create a new PR or update this one?

[oliviertassinari]

Should I create a new PR or update this one?

What's the advantage of opening a new one? You can simply update this one.
Regarding the whitelist of components that the Menu should be highjacking, I haven't looked in detail but I believe MenuItem is the only one. We could be using node.type.muiName === 'MenuItem' as we do with the other components.