Reduce ISO size

We need to reduce the ISO size to stay under the 2GB limit for GitHub Releases yet give us some headroom.

Useful commands:

### See a tree of the top-level dependencies

```
sudo pkg -y install pkg pkg_tree
pkg_tree
```

This gives a quick overview about the _direct_ dependencies of all installed packages.

### See why a package was included

Example:

`pkg remove -n perl5` (this needs no root rights and does not do anything besides print the information)

This shows which other packages we would have to sacrifice if we wanted to get rid of the `perl5` package.

### See why something is an indirect dependency of something

Example:

```
pkg_tree -v zenity > zenity.deps
```

This produces a huge tree, so it is best to redirect the output of a file where it can be searched.