Do not reference the underspecified (and generally discouraged) BIP 69

[TheBlueMatt]

Instead of saying that transactions should follow BIP 69, we should write out what that means, given BIP 69 isn't even well-specified itself (and to avoid the implied support for BIP 69, which generally is strongly discouraged for things that don't look like Lightning). See-also lightningdevkit/rust-lightning#84

[rustyrussell]

Do you have a reference for BIP 69 being strongly discouraged? I've considered we should go the other way and make it compulsory, but that requires a replacement for SIGHASH_SINGLE, which means never...

Either way, we'll be dealing with this explicitly in #448 because it turns out ordering everything canonically requires more than knowing the tx...