The new param ampCors: boolean introduced by #6637 should replace the existing requireAmpResponseSourceOrigin.

No new code should specify requireAmpResponseSourceOrigin. Rather, they should use ampCors: false to turn off AMP CORS, which means no __amp_source_origin in XHR URL, and no check for AMP_SOURCE_ORIGIN response header.

We will make ampCors defaults to true. (Or false? @cramforce thoughts? Do we encourage people to enable AMP CORS?).

For backward compatibility, will change the existing code to include requireAmpResponseSourceOrigin: false explicitly if they still want the __amp_source_origin in request, but no check for response.