DOC: Remove latest whatsnew from header
In favor of going via the "Release notes" which stays in the header.

Closes https://github.com/pandas-dev/pandas/issues/32748
Nice, thanks @TomAugspurger  Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
$ git checkout 1.0.x
$ git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
$ git cherry-pick -m1 f76763fe741cf5c7e0a4c69faef319e437f475e5
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
$ git commit -am 'Backport PR #32870: DOC: Remove latest whatsnew from header'
```

4. Push to a named branch :

```
git push YOURFORK 1.0.x:auto-backport-of-pr-32870-on-1.0.x
```

5. Create a PR against branch 1.0.x, I would have named this PR:

> "Backport PR #32870 on branch 1.0.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                