bpo-45020: Drop the frozen .h files from the repo. (gh-28392)

bpo-45020: Drop the frozen .h files from the repo. (gh-28392)

The main advantage is that the files will no longer show up in diffs and PRs. That means, for a PR, the number of files / lines changed will more clearly reflect the actual change.  (This is essentially an un-revert of gh-28375.)

https://bugs.python.org/issue45020