Stop polluting configuration object in w3c/headers.js

[saschanaz]

Currently it pollutes the configuration object only to pass them to templates. They should be instead passed as a dictionary object.

[marcoscaceres]

Agree! and we should identify other modules that do this. So 🤮

[sidvishnoi]

I think core/caniuse.js is another potential candidate

[saschanaz]

@sidvishnoi It looks like core/caniuse just normalizes the user configurable fields, which should be okay.