asus-me176c: remove -x11 subpackage (!917)

So far, the -x11 subpackage for asus-me176c was used to install
the Xorg Intel driver (xf86-video-intel). But these days many
distributions actually recommend using the standard Xorg modesetting
driver instead, see e.g.
  - Debian: https://tjaalton.wordpress.com/2016/07/23/intel-graphics-gen4-and-newer-now-defaults-to-modesetting-driver-on-x/
  - Fedora: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/AUPYPJMFJZMHPEKN24LBABZKIEOV4NU5/
  - KDE: https://community.kde.org/Plasma/5.9_Errata#Intel_GPUs

The standard Xorg modesetting driver is included in the main xorg-server
package. Not installing xf86-video-intel saves about ~73 MiB of disk space
(because it also pulls in many unneeded dependencies).

Xfce seems to be working just fine with the modesetting driver.
(And most users will probably prefer Wayland anyway...)