Remove or comment `recent_measurement_attempt` KeyValue in the bandwidth-file-spec.txt

In tpo/network-health/sbws!34 (merged) we have removed the KeyValue, to avoid sbws crashing cause it can't handle that big amount of json data (tpo/network-health/sbws#40020 (closed)) and maybe making sbws (tpo/network-health/sbws#40020 (closed)).

We should remove that KeyValue in the specification (new version?) or comment it's removed from sbws version 1.1.0+161.g8fdd85b7

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