discovery+server: make waiting proofs persistent

In this commit waiting proofs array have been replaced with persistant
boltd storage which removes the possibility for the half proof to be
lost during half proof exchange.

discovery/utils.go

@@ -1,8 +1,6 @@
 package discovery
 
 import (
-	"encoding/binary"
-
 	"github.com/go-errors/errors"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnwallet"
@@ -10,31 +8,6 @@ import (
 	"github.com/roasbeef/btcd/btcec"
 )
 
-// newProofKey constructs a new announcement signature message key.
-func newProofKey(chanID uint64, isRemote bool) waitingProofKey {
-	return waitingProofKey{
-		chanID:   chanID,
-		isRemote: isRemote,
-	}
-}
-
-// ToBytes returns a serialized representation of the key.
-func (k waitingProofKey) ToBytes() []byte {
-	var key [9]byte
-
-	var b uint8
-	if k.isRemote {
-		b = 0
-	} else {
-		b = 1
-	}
-
-	binary.BigEndian.PutUint64(key[:8], k.chanID)
-	key[8] = b
-
-	return key[:]
-}
-
 // createChanAnnouncement is a helper function which creates all channel
 // announcements given the necessary channel related database items. This
 // function is used to transform out databse structs into the coresponding wire