What happened to "Allow commits from members who can merge to the target branch."?

[Simon Redman]

Hi all,

Previously when making a PR, I was able to select a checkbox to allow 
others to merge to my PR branch:


Now, that box seems to have vanished.

Did I miss a discussion about removing this feature? It's super useful 
so that I can do small fixups to a stale PR and then merge it.

Thanks,
Simon