We actually do need this for dualopend's, specifically for returning errors to open_channel2
v2 of channel open uses the channel revocation basepoints to calculate the channel_id, instead of the funding_txid + outnum Moving away from the funding_txid opens the way for splicing + rbf
The definition was in wire/wire.h, and helper functions in fromwire.c! Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>