CH02::Bobs view: remove tipbox about unconfirmed safety

This advice may have been somewhat accurate when the first edition of
this book was published and opt-in replace-by-fee wasn't available, but
that's no longer the case.  And now, especially, with default
replace-by-fee on the probable horizon, there's even less safety in
accepting unconfirmed transactions as final without some type of
secondary protection.

ch02.asciidoc

@@ -509,20 +509,6 @@ transaction through other nodes, it will reach Bob's wallet within a few
 seconds. Bob's wallet will immediately identify Alice's transaction as
 an incoming payment because it contains an output redeemable by Bob's
 keys. Bob's wallet application can also independently verify that the
-
-[TIP]
-====
-((("confirmations", "of small-value transactions",
-secondary-sortas="small-value transactions")))A common misconception
-about bitcoin transactions is that they must be "confirmed" by waiting
-10 minutes for a new block, or up to 60 minutes for a full six
-confirmations. Although confirmations ensure the transaction has been
-accepted by the whole network, such a delay is unnecessary for
-small-value items such as a cup of coffee. A merchant may accept a valid
-small-value transaction with no confirmations, with no more risk than a
-credit card payment made without an ID or a signature, as merchants
-routinely accept today.((("", startref="Tconstruct02")))
-====
 transaction is well formed.  If Bob is using his own full node, his
 wallet can further verify Alice's transaction only spends valid UTXOs.