[configs/releng] Use drop-in feature of systemd for getty autologin

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

configs/releng/root-image/etc/systemd/system/getty@tty1.service.d/autologin.conf

+[Service]
+ExecStart=
+ExecStart=-/sbin/agetty --autologin root --noclear %I 38400 linux

configs/releng/root-image/root/customize_root_image.sh

@@ -17,9 +17,4 @@ chmod 440 /etc/sudoers.d/g_wheel
 
 sed -i "s/#Server/Server/g" /etc/pacman.d/mirrorlist
 
-sed 's#\(^ExecStart=-/sbin/agetty\)#\1 --autologin root#;
-     s#\(^Alias=getty.target.wants/\).\+#\1autologin@tty1.service#' \
-     /usr/lib/systemd/system/getty@.service > /etc/systemd/system/autologin@.service
-
-systemctl disable getty@tty1.service
-systemctl enable multi-user.target pacman-init.service autologin@.service dhcpcd.service
+systemctl enable multi-user.target pacman-init.service dhcpcd.service