Consistent JSON format

[engn33r]

I see results/codearena_findings.json has a separate "target" field that does not exist in the other JSON findings formats. I expect this field should be deleted from codearena_findings.json for consistency.

[engn33r]

Another inconsistency is that some results JSON files have the word "Severity:" in the label for risk level, like ToB, but other JSON files, like code4rena, do not have the word "Severity:".

[joswha]

the target field in the codearena_findings is kept there for ease of search via regex; one solution to this issue will be adding the target as part of the labels array.