Generally this means converting a lazy "peer_active_channel(peer)" call
into an explicit iteration.
1. notify_feerate_change: call all channels (ignores non-active ones anyway).
2. peer_get_owning_subd remove unused function.
3. peer_connected hook: don't save channel, do lookup and iterate channels.
4. In json_setchannelfee "all" remove useless call to peer_active_channel
since we check state anyway, and iterate.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>