Switch to the new go-db-xrefs.json produced on @geneontology/go-site

[kltm]

As stated, switch to the new go-db-xrefs.json produced on kltm/go-site. This depends on geneontology/go-site#33.

[kltm]

Well, since we're about to switch to the new upstream geneontology/go-site/metadata/db-xrefs.yaml, this will be pushed down the road a little. Punt to 2.3.

[kltm]

@cmungall , before I close this out (as it seems to be no worse than the current implementation), I wanted to ask about this:

https://github.com/geneontology/go-site/blob/master/metadata/db-xrefs.yaml#L2326
http://amigo.geneontology.org/xrefs#TAIR

AmiGO currently does not really use entity types, just the database name for the look ups. However, that means that for things like TAIR, we're just using the last one for the map. Is that acceptable behavior? I seems to be the current behavior, and I'm not sure of an easy fix, but it might be good to talk about it.