Do not download a mirrorlist durring build

Pacman's mirrolist will be updated by reflector.service in the live system.

configs/releng/build.sh

@@ -120,9 +120,6 @@ make_customize_airootfs() {
 
     cp "${script_path}/pacman.conf" "${work_dir}/x86_64/airootfs/etc"
 
-    curl -o "${work_dir}/x86_64/airootfs/etc/pacman.d/mirrorlist" \
-        'https://www.archlinux.org/mirrorlist/?country=all&protocol=http&use_mirror_status=on'
-
     lynx -dump -nolist 'https://wiki.archlinux.org/index.php/Installation_Guide?action=render' >> \
         "${work_dir}/x86_64/airootfs/root/install.txt"