* Remove the manual download of CGAL from setup.py.
* Remove '--with-cgaldir' autogen.sh flag as CGAL should be installed
  in a location by the package managers or user that it is findable.

* The cibuildwheel Linux container is CentOS 7 based, but CGAL is
  not packaged for CentOS with yum --- only for apt-get, Homebrew,
  and conda-forge. For Linux cibuildwheel builds this then requires
  that the CGAL headers (CGLA is header only) need to be manually
  downloaded from GitHub and then copied into /usr/include/.

* Add libcgal-dev to the required packages to install for Linux based
  development.

* Use package managers to install libcgal-dev (Linux) and cgal (macOS)
  in CI jobs.

…-cgal-header-only'


From `./configure --help`:

```
  --enable-cgal           enables link with the CGAL library default=no
  --enable-cgal-header-only   enable build with header-only install of CGAL, e.g. as for CGALv5; in that case do not use --enable-cgal default=no
```

…--enable-cgal-header-only'"

This reverts commit 363f100.