rfqmsg: remove unused RFQ reject message error types

Eliminating these error types ensures that all current errors align with
those documented in the BLIP.

rfqmsg/reject.go

@@ -103,20 +103,6 @@ var (
 		Code: 1,
 		Msg:  "price oracle unavailable",
 	}
-
-	// ErrNoSuitableSellOffer is the error code for when there is no
-	// suitable sell offer available.
-	ErrNoSuitableSellOffer = RejectErr{
-		Code: 2,
-		Msg:  "no suitable sell offer available",
-	}
-
-	// ErrNoSuitableBuyOffer is the error code for when there is no suitable
-	// buy offer available.
-	ErrNoSuitableBuyOffer = RejectErr{
-		Code: 3,
-		Msg:  "no suitable buy offer available",
-	}
 )
 
 const (

rfqmsg/reject_test.go

@@ -31,14 +31,20 @@ func TestRejectEncodeDecode(t *testing.T) {
 			peer:    route.Vertex{1, 2, 3},
 			version: 0,
 			id:      id,
-			err:     ErrNoSuitableSellOffer,
 		},
 		{
 			testName: "all fields populated with basic values",
 			peer:     route.Vertex{1, 2, 3},
 			version:  5,
 			id:       id,
-			err:      ErrNoSuitableBuyOffer,
+		},
+		{
+			testName: "all fields populated with basic values; " +
+				"error field populated",
+			peer:    route.Vertex{1, 2, 3},
+			version: 5,
+			id:      id,
+			err:     ErrPriceOracleUnavailable,
 		},
 	}