Clarification of Elasticsearch Versions

The documentation here says any version 2.4+ with the Delete By Query plugin. However, it seems, they removed that plugin in favor of a core-API (here and here). So, should GitLab EE be updated to use the new Core API in recent versions of Elasticsearch (which would raise the minimum version required by GitLab EE), or should a "maximum version" be noted, as the plugin is removed in later versions entirely.

cc: @dblessing