Update btp2 extension document.
Remove proof in BTPHeader
@@ -421,7 +421,6 @@ BTPBlockHeader is `B_LIST` of the following fields
| Prev | B_BYTES(N) | H(NetworkSection) of prev BTP block |
| MessageCount | B_INT | |
| MessagesRoot | B_BYTES(N) | Merkle root of Messages |
-| Proof | B_BYTES | proof bytes of H(NetworkTypeSectionDecision) |
| NextProofContext | B_BYTES(N) | nil if NextProofContextHash is the same as previous block's value. non-nil if Prev is nil |
### MerkleNode
