cibuildwheel: remove useless pp* skip selector
Since cibuildwheel 3.0.0 pypy builds are no longer enabled by default
[1]. We can remove the skip selector. This will also fix the following
warning during build:
Warning: cibuildwheel: Invalid skip selector: 'pp*'. This selector matches a group that wasn't enabled. Enable it using the `enable` option or remove this selector. This selector will have no effect.
[1]: https://cibuildwheel.pypa.io/en/stable/changelog/#v300
Signed-off-by: Julien Stephan <jstephan@baylibre.com>