message: Fix comment about s in schnorr sigs
  Summary: s/order/n/ for consistency.
  Test Plan: None
  Reviewers: markblundeberg, O1 Bitcoin ABC, #bitcoin_abc, deadalnix, Fabien, jasonbcox
  Subscribers: schancel
diff: * public key point P,
  * signature: (32-byte r, scalar s)
  *
  - * Signature is invalid if s >= order or r >= p.
  + * Signature is invalid if s >= n or r >= p.
  * Compute scalar e = Hash(r || compressed(P) || m) mod n.
  * Option 1 (faster for single verification):
  * Compute point R = s * G - e * P.
  