Allow retracting autoflag from chat

[j-f1]

It would be great to add a button on Smokey’s report to retract the autoflag if you were chosen as the flagger. In fact, it could be a set of buttons: a checkmark to mark the post as tpu-, and an x to mark the post as fp- and retract the flag.

[Undo1]

We don't have a way to retract flags from the API, we'd need http://meta.stackexchange.com/q/288120/215468 to be implemented.

[j-f1]

This can be done if the user’s fkey is known:

$.post(`/flags/posts/${postId}/retract/${flagType}`, {
  fkey: StackExchange.options.user.fkey
})

I could definitely get the fkey in Coal, so this could be a feature there.

[ArtOfCode-]

@j-f1 Trip hazard: chat fkeys are different to main-site fkeys.