Simplify proposal msg (#2735)

* Align Proposal message with spec

* Update spec

types/proposal.go

@@ -15,43 +15,41 @@ var (
 )
 
 // Proposal defines a block proposal for the consensus.
-// It refers to the block only by its PartSetHeader.
+// It refers to the block by BlockID field.
 // It must be signed by the correct proposer for the given Height/Round
 // to be considered valid. It may depend on votes from a previous round,
-// a so-called Proof-of-Lock (POL) round, as noted in the POLRound and POLBlockID.
+// a so-called Proof-of-Lock (POL) round, as noted in the POLRound.
+// If POLRound >= 0, then BlockID corresponds to the block that is locked in POLRound.
 type Proposal struct {
-	Type             SignedMsgType
-	Height           int64         `json:"height"`
-	Round            int           `json:"round"`
-	POLRound         int           `json:"pol_round"` // -1 if null.
-	Timestamp        time.Time     `json:"timestamp"`
-	BlockPartsHeader PartSetHeader `json:"block_parts_header"`
-	POLBlockID       BlockID       `json:"pol_block_id"` // zero if null.
-	Signature        []byte        `json:"signature"`
+	Type      SignedMsgType
+	Height    int64     `json:"height"`
+	Round     int       `json:"round"`
+	POLRound  int       `json:"pol_round"` // -1 if null.
+	BlockID   BlockID   `json:"block_id"`
+	Timestamp time.Time `json:"timestamp"`
+	Signature []byte    `json:"signature"`
 }
 
 // NewProposal returns a new Proposal.
 // If there is no POLRound, polRound should be -1.
-func NewProposal(height int64, round int, blockPartsHeader PartSetHeader, polRound int, polBlockID BlockID) *Proposal {
+func NewProposal(height int64, round int, polRound int, blockID BlockID) *Proposal {
 	return &Proposal{
-		Type:             ProposalType,
-		Height:           height,
-		Round:            round,
-		POLRound:         polRound,
-		Timestamp:        tmtime.Now(),
-		BlockPartsHeader: blockPartsHeader,
-		POLBlockID:       polBlockID,
+		Type:      ProposalType,
+		Height:    height,
+		Round:     round,
+		BlockID:   blockID,
+		POLRound:  polRound,
+		Timestamp: tmtime.Now(),
 	}
 }
 
 // String returns a string representation of the Proposal.
 func (p *Proposal) String() string {
-	return fmt.Sprintf("Proposal{%v/%v %v (%v,%v) %X @ %s}",
+	return fmt.Sprintf("Proposal{%v/%v (%v, %v) %X @ %s}",
 		p.Height,
 		p.Round,
-		p.BlockPartsHeader,
+		p.BlockID,
 		p.POLRound,
-		p.POLBlockID,
 		cmn.Fingerprint(p.Signature),
 		CanonicalTime(p.Timestamp))
 }