Remove redundant key/value pairs from config.json
Remove redundant key/value pairs from config.json

The slug is not used anywhere. We initialize a track based on knowing the Track ID.
Since the repository is always named after the track ID, this field, too, is redundant,
as it can be inferred.

exercism/xjava,jmluy/xjava,exercism/xjava,FridaTveit/xjava,FridaTveit/xjava,jmluy/xjava