CH05::remove web-based BIP39 generator/editor

Even in the hands of an expert, the security of these things is dubious.
When used by a novice, there's a pretty high chance of them leaking or
breaking their keys.

ch05.asciidoc

@@ -826,19 +826,6 @@ https://github.com/libbitcoin/libbitcoin/blob/master/src/wallet/mnemonic.cpp[lib
 An implementation of BIP39, as part of the popular Libbitcoin
 framework, in pass:[<span class="keep-together">C++</span>]
 
-There is also a BIP39 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 BIP39 generator as a standalone web page
-image::images/mbc2_0508.png["BIP39 generator web-page"]
-
-((("", startref="mnemonic05")))((("", startref="BIP3905")))The page
-(https://iancoleman.github.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