Removes es6 (es5 and es2).

[ghost]

Refs inveniosoftware/invenio-records-resources#305

[slint]

Unfortunately, this is a very "old" module that didn't receive any love in terms of modernizing to use docker-services-cli and other best practices for GitHub CI.

On the other hand, it's also a very "special" module, since it's also testing e.g. cross-cluster migration of indices, so I'm not even sure if we could test it using our usual methods.

@chriz-uniba are you using this module actively for migrating indices? It's pretty rough on the edges still since it was originally developed as a common solution between some of our Invenio instances at CERN to help with migrating/upgrading our search clusters with minimal downtime. Eventually it might be used for InenioRDM to perform mapping upgrades across versions, but it's very early to tell.

[ghost]

there was an open issue wrt. elasticsearch and I worked on it in every https://github.com/inveniosoftware/ I could find references to old elasticsearches. Feel free to close or ignore. ;)

[slint]

Thanks for the explanation, I'm closing it then :)