files: remove HTTP code from read_content

* 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.

invenio_records_resources/resources/files/resource.py

@@ -201,7 +201,7 @@ def read_content(self):
         if obj is not None and emitter is not None:
             emitter(current_app, record=item._record, obj=obj, via_api=True)
 
-        return item.send_file(), 200
+        return item.send_file()
 
     @request_view_args
     def read_archive(self):