Clean up TODO comment after issue closed

[sana-ajani]

From Twitter: https://twitter.com/alvaromartmart/status/1278759499894054912

Not sure if we can remove the TODO, but that would be helpful to "close the loop". Perhaps we could trigger the code action again reminding users it's still there?

[egamma]

We could validate that a TODO still applies when it is open in an editor. The validation would check whether the issue is still open, if it is closed we could squiggle the TODO with a diagnostic warning.