discogs: restore strip of disambiguation number from artist

[kergoth]

The integration of MetadataSourcePlugin removed the strip, as it's
discogs specific, but converted discogs to use it, which is a problem.
Restore our own get_artist which makes the per-artist change we need.

[kergoth]

Without this fix, we get entries in the candidates list like this (note the (2) suffix:

4. Patrick Watson (2) - Wooden Arms (49.1%) (missing tracks, source, ...) (Discogs, CD, 2009, Canada, Secret City Records, SCR012CD)                                        
5. Patrick Watson (2) - Wooden Arms (49.1%) (missing tracks, source, ...) (Discogs, CD, 2009, Benelux, V2, VVNL20762)                                                       
6. Patrick Watson (2) - Wooden Arms (49.1%) (missing tracks, source, ...) (Discogs, CD, 2009, France, Tôt Ou Tard, 8345 10659 2)

[kergoth]

I'm not sure how generally useful this get_artist method is going to be, but if we think it is, we might want to separate the 'get the list of artists' from the join, to let the caller manipulate the individual artists rather than only getting the merged string.

[rhlahuja]

Hey @kergoth you're right, I realized I mistakenly removed that bit of logic from but have added it back in #3389 over here. That PR also integrates it in the Beatport plugin, since the logic is identical.

I don't anticipate this to be an issue for metadata sources which don't include disambiguation numbers, unless we actually encounter an artist named e.g. Artist (1). Although if we do, I agree returning a list of artists makes more sense for the API.

[kergoth]

Ah, excellent, I didn’t notice that one. Thanks!