I can confirm that the above method does NOT work for Nexus 5. I have KitKat 4.4.4 and I want to get rid of the 5.0 update notification (which I previously installed and which is slower, compared to 4.4.4). The "com.google.android.gsf.update.SystemUpdateService$Receiver" function is already disabled by default in 4.4.4, along with the other update functions in this group. So basically I have nothing to check off.
This method works, finally. I did as suggested, I checked off the "show notification" in Google Play Services app and the OTA update notification is gone. But so are gone the app update notifications, but I can live with that.
If anyone knew how to strictly apply the first method by disabling a specific receiver, it would be awesome though. Thanks a lot.
UPDATE: Finally, I have managed to get rid of the OTA update notification on Nexus 5 4.4.4 without completely removing Google Play Services notifications. I actually used WooHooGuy's method but I dug deeper. The aforementioned "SystemUpdateService" receivers (in KitKat 4.4.4) are actually located now under the Google Play Services receivers group; what I did was to search for all items containing System Update under the Google Play Services tab and I disabled them all. The effect is not instant; I had to hit a restart; after my Nexus 5 had restarted, I had no OTA update notification anymore in the notifications area. This is WooHooGuy's merit, thanks a lot. Also I used Infernal Satan's idea, as I found out that the app responsible for that notification was Google Play Services, and not Google Framework/system. I am now a happy Nexus 5 rooted user.