Update for those who are using XFCE
Recently xfce4-notifyd has become a "must" and not a "make" dependency for xfce4-power-manager.
This means when you'll do a system upgrade the package - xfce4-notifyd will get installed and override the current notification-center.
If you want to stick with the current notification-center then go to settings> session and startup > application autostart > uncheck the option that says: XFCE notification-daemon.
If you are not ok with the current notification-center then 1. Either leave it as it is since xfce4-notifyd has overridden it.
2. Or, go to application autostart again and this time uncheck: notification-center (6 option most likely )
Sudo pacman -Rdns deadd-notification-center-git
Note: to customize xfce4-notifyd do:
Ctrl+r > type notification > hit enter