Remove external_id from table view and filters

See https://aptivate.kanbantool.com/b/437721-internews-hid-2018#27567031.

I opted to go with the HTML comment hack because removing external_id from the configuration forces the code logic to start to exclude it in every aspect, including the importer. The importer fails to import _uuid fields and a lot of tests fail. Any change within the import logic was not mentioned, so I assume this is just a cosmetic thing. Also, going this route avoids to have anyone need to manually update configurations on existing deployments (or write data migrations).

CI failure is not related and is "fixed" by !142 (diffs).