vagrant: Remove unneeded netctl

netctl isn't used since Vagrant v2.2.10[1][2] and the users has been
given a fair chance to update now (>9 months).

Fix #112

[1] https://github.com/hashicorp/vagrant/blob/ee2a5daceec7f18accc59a69b84ced299a219188/CHANGELOG.md#2210-august-24-2020
[2] https://github.com/hashicorp/vagrant/pull/11400

images/common.sh

 #!/bin/bash
 
 function vagrant_common() {
-  arch-chroot "${MOUNT}" /usr/bin/pacman -S --noconfirm netctl polkit
+  arch-chroot "${MOUNT}" /usr/bin/pacman -S --noconfirm polkit
 
   local NEWUSER="vagrant"
   # setting the user credentials