Changed update CC thresholds to 51%

[kevinhammond]

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This PR updates the thresholds and comments for the "Update constitutional committee action" in defaultConstitution.json to reflect a late guardrail change from 65% to 51%.

The original high-level guardrail was:

"Update Constitutional committee action thresholds must be in the range 65%-90%"
The new guardrail is:

"Update Constitutional committee action thresholds must be in the range 51%-90%"

Four guardrails are affected: for DReps or for SPOs in both Confidence and No Confidence states

[bezirg]

Closed in favor of #6320