New review comment by classabbyamp on void-packages repository

https://github.com/void-linux/void-packages/pull/39984#discussion_r997533534

Comment:
```suggestion
post_extract() {
	cd $XBPS_BUILDDIR
	bsdtar -xvf ${pkgname}${version}.tar
	rm -rf CalculiX
	rm ${pkgname}${version}.tar
```
overriding `do_extract` should be a last resort, and this is a bit cleaner anyways