Fix scripthash subscribe status hash byte order

[eynhaender]

Fix blockchain.scripthash.subscribe status hash byte order

encode_hash() reverses bytes (Bitcoin txid display format); Electrum protocol requires the SHA256 status in natural byte order. Replace with encode_base16() in complete_scripthash_subscribe and scripthash_notify.

From the Electrum protocol docs:

"The status of the script hash is the sha256() hash of the full string
expressed as a hexadecimal string … in its natural byte order (not reversed)."