Remove dfuse check from bp.json validator tool

[UrsaPolarisRecords]

Current bp.json enumerates the "dfuse" validation check. See at URL https://validate.eosnation.io/eos/producers/

EOS Nation no longer supports dfuse, and neither does any other BP. We should likely remove it.

I see dfuse enumerated in the code here. It may be elsewhere too.

https://github.com/EOS-Nation/bpvalidate/blob/0d64fcb8a40f4f226940eeca1bb09b5c8bd88de8/config/schema.json#L281C16-L281C25

[UrsaPolarisRecords]

Argument against removing it: if another BP decides they'd like to support dfuse, then we don't have to go back and add it in later. Also, if any users are looking for dfuse endpoints, this will confirm for them that those endpoints are nowhere to be found.

Argument for: dfuse is gone, might as well get rid of it