Remove invalid extra commas from json data

[pavoljuhas]

Ensure all json files pass the following validation

$ git ls-files *.json |
    while read f; do python -m json.tool $f >/dev/null || echo $f; done

[viathor]

(If you're going to rely on this, consider adding a CI check.)

[pavoljuhas]

(If you're going to rely on this, consider adding a CI check.)

Ack. I noticed this when reviewing a recent change in asv.conf.json where my editor highlighted syntax error.
Only 2 out of 256 json files failed validation with json.tool. I feel a CI check is not quite warranted.