code: func NewDelAttributeClaim(permaNode blob.Ref, attr, value string) *Builder {
  	return newClaim(&claimParam{
  		permanode: permaNode,
  		claimType: DelAttributeClaim,
  		attribute: attr,
  		value:     value,
  	})
  }
docs: // NewDelAttributeClaim creates a new claim to remove value from the
  // values set for the attribute attr of permaNode. If value is empty then
  // all the values for attribute are cleared.