Discogs: Featured artists appear twice.

[henry-oberholtzer]

On the current implementation of the discogs plugin, for supporting featured artists, the plugin does not account for cases where an artist may be credited as featured in the artist name, and also in the track credits.

When importing this album:, track 6 ends up with duplicate credits. Discogs current has the track credited as follows.

6 - Filteria Feat. Ukiro - Infinite Regression
    Written-By, Producer, Featuring – Ukiro

On import, it results in the following:

Filteria Feat. Ukiro Feat. Ukiro - Infinite Regression

The provided Discogs information may be redundant, but there doesn't seem to be a concise guideline on whether it's a database violation either, so I think we will have to figure out a way to handle it.