files: remove HTTP code from read_content

[egabancho]

• Setting the return code directly hides the return code that send_file might be issuing, resulting in odd situations when the storage layer returns a 302, i.e. offload download.

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When an instance uses local storage, eventually send_file gets called and the file is streamed through the application server.

If one uses Invenio-S3, instead of serving the file directly, the application issues a redirect to a short-lived signed URL, relaying the work of streaming the file to the storage server, offloading.

The problem is that send_file itself returns a response with its own response code, etc. The 200 here basically overwrites that response code and the redirect doesn't work.

We don't experience that same behavior with EOS because the redirect is happening at nginx level using X-Accel-Redirect.

[egabancho]

This should probably fix inveniosoftware/invenio-app-rdm#2017 🤔

[tmorrell]

This broke uploads on my (fairly ancient) test system

flask_resources/responses.py", line 40, in inner
   return resource_requestctx.response_handler.make_response(*res, many=many)
TypeError: make_response() got multiple values for argument 'many'

and didn't seem to fix the content issue. I'll try to test on v13 soon and see if it works better there.

[egabancho]

I tested it locally on v13.0.0b1.dev25, and I didn't get any error.
How did you test it? Did you check-pick the change?