removes unused first height field from LN builder

This field reads the first height of an epoch, which may be unavailable
if the node is using Dynamic Bootstrap.

module/builder/collection/builder.go

@@ -43,9 +43,8 @@ type Builder struct {
 	log            zerolog.Logger
 	clusterEpoch   uint64 // the operating epoch for this cluster
 	// cache of values about the operating epoch which never change
-	refEpochFirstHeight uint64           // first height of this cluster's operating epoch
-	epochFinalHeight    *uint64          // last height of this cluster's operating epoch (nil if epoch not ended)
-	epochFinalID        *flow.Identifier // ID of last block in this cluster's operating epoch (nil if epoch not ended)
+	epochFinalHeight *uint64          // last height of this cluster's operating epoch (nil if epoch not ended)
+	epochFinalID     *flow.Identifier // ID of last block in this cluster's operating epoch (nil if epoch not ended)
 }
 
 func NewBuilder(
@@ -75,11 +74,6 @@ func NewBuilder(
 		clusterEpoch:   epochCounter,
 	}
 
-	err := db.View(operation.RetrieveEpochFirstHeight(epochCounter, &b.refEpochFirstHeight))
-	if err != nil {
-		return nil, fmt.Errorf("could not get epoch first height: %w", err)
-	}
-
 	for _, apply := range opts {
 		apply(&b.config)
 	}