I tried Android 5 (lollipop) on my Nexus5 and did not like it, so I reverted to Android 4 (kitkat). System Updated Available notifications could not be dismissed. Here is how to deactivate them.
1. Open Settings
2. Select Apps
1. Slide tab menus right to "ALL"
2. Scroll down to "Google Play services"
3. Tap to open
1. Uncheck the "Show notifications"
2. Click "OK" on the "Turn off notifications?" warning Pop Up Ad
The notifications will cease.
The "Show notifications" box will stop for "Google Play services" (only)
Only {System Available Update} and "Google Play services" notifications will be banned.