For compatibility, we only do this if `allow-deprecated-apis` is false
for now. Otherwise scripts parsing should use `grep -v '^# '` or
start using `-N none`.
Changelog-Added: JSON-RPC: `close` now sends notifications for slow closes (if `allow-deprecated-apis`=false)
Changelog-Deprecated: cli: scripts should filter out '^# ' or use `-N none`, as commands will start returning notifications soon
Fixes: #3925
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>