fix: remove docker from defaults, fix cliphist-image ordering cycle

Docker is a dev dependency, not a desktop environment default. Remove
from package list, archinstall config, services and README.

Fix systemd ordering cycle that prevented cliphist-image from starting:
cliphist-text had After=graphical-session.target which combined with
PartOf= and cliphist-image's After=cliphist-text created a cycle.

scripts/post-install.sh

@@ -144,7 +144,6 @@ log "Enabling services..."
 SERVICES=(
     "NetworkManager"
     "bluetooth"
-    "docker"
     "greetd"
     "systemd-timesyncd"
     "ufw"