Drop unmaintained /etc/skel/.w3m/config

This file was unmodified for >15 years and Debian's w3m package includes
a /etc/w3m/config configuration file which lists more configuration
settings and plenty of the options diverge slightly from our
configuration. Let's drop our configuration file and use Debian's
defaults (if we really want to change specific settings let's identify
those and we could then only overwrite those specific settings instead
of shipping a full and poorly maintained configuration file).