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

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?