CH08: drop paragraph about segwit commiting to input amount

This now has a well-known problem and doesn't provide the guarantees
that were hoped for.

chapters/signatures.adoc

@@ -408,17 +408,7 @@ the way the commitment hash is calculated. For segwit version 0 witness
 programs, signature verification occurs using an improved commitment
 hash algorithm as specified in BIP-143.
 
-The new algorithm achieves two important goals. Firstly, the number of
+The new algorithm allows the number of
 hash operations increases by a much more gradual O(n) to the number of
 signature operations, reducing the opportunity to create
-denial-of-service attacks with overly complex transactions. Secondly,
-the commitment hash now also includes the value (amounts) of each input
-as part of the commitment. This means that a signer can commit to a
-specific input value without needing to "fetch" and check the previous
-transaction referenced by the input. In the case of offline devices,
-such as hardware wallets, this greatly simplifies the communication
-between the host and the hardware wallet, removing the need to stream
-previous transactions for validation. A hardware wallet can accept the
-input value "as stated" by an untrusted host. Since the signature is
-invalid if that input value is not correct, the hardware wallet doesn't
-need to validate the value before signing the input.
+denial-of-service attacks with overly complex transactions.