Remove operating systems that are not entirely free

[johnjago]

Since awesome lists are supposed to be lists of the best, not of everything, let's remove all operating systems that are not entirely free software.

You should rather leave stuff out than include too much.

After all, it's a curation, not a collection.

Here is a reference to get started: https://www.gnu.org/distros/free-distros.html

The note about some operating systems containing non-free components at the top of the OS section can then be removed.