ch05: Don't use web pages to generate mnemonics

Due to the recent controversy regarding bitcoinpaperwallet.com,
recommending we don't even point people to places where they can use
webpages to generate private keys and/or mnemonics.

ch05.asciidoc

@@ -293,14 +293,6 @@ https://github.com/bitcoinjs/bip39[bitcoinjs/bip39]:: An implementation of BIP-3
 
 https://github.com/libbitcoin/libbitcoin/blob/master/src/wallet/mnemonic.cpp[libbitcoin/mnemonic]:: An implementation of BIP-39, as part of the popular Libbitcoin framework, in pass:[<span class="keep-together">C++</span>]
 
-There is also a BIP-39 generator implemented in a standalone webpage, which is extremely useful for testing and experimentation. <<a_bip39_generator_as_a_standalone_web_page>> shows a standalone web page that generates mnemonics, seeds, and extended private keys.
-
-[[a_bip39_generator_as_a_standalone_web_page]]
-.A BIP-39 generator as a standalone web page
-image::images/mbc2_0508.png["BIP-39 generator web-page"]
-
-((("", startref="mnemonic05")))((("", startref="BIP3905")))The page (https://iancoleman.io/bip39/) can be used offline in a browser, or accessed online.
-
 ==== Creating an HD Wallet from the Seed
 
 ((("wallets", "technology of", "creating HD wallets from root seed")))((("root seeds")))((("hierarchical deterministic (HD) wallets")))HD wallets are created from a single _root seed_, which is a 128-, 256-, or 512-bit random number. Most commonly, this seed is generated from a _mnemonic_ as detailed in the previous section.