Delete the legacy `pages-build-deployment` github action

[kenzieschmoll]

Link: https://github.com/flutter/devtools/actions/workflows/pages/pages-build-deployment

This is a legacy action that was for the old Jekyll-based documentation. These docs haven't been used in years, and the redirects were recently deleted from our repo, which is why the github action is now failing.

I cannot see a way to delete the action. Maybe I don't have permissions? @Piinks or @devoncarew do you know how we can delete this action from the flutter/devtools repo?

[DanTup]

Possibly it's configured in the Repo settings here? (the action name matches the one I see for Dart-Code's website which is configured there):

[kenzieschmoll]

Thanks, Danny. I do not have access to change the repo settings. Do you, @Piinks?

[devoncarew]

Perhaps the workflow definition is coming from a branch other than master?

I see a lot of stale branches here: https://github.com/flutter/devtools/branches. You might clean those up and see if the workflow doesn't just disappear (it would also be worth enabling the repo setting to auto delete merged branches).

[DanTup]

I don't think pages-build-deployment comes from a workflow in the repo, I think it's special (there aren't any workflows in https://github.com/Dart-Code/Website but it still has that action running - https://github.com/Dart-Code/Website/actions)