Fix various issues with loading os definitions (#11640)

* Ping only device doesn't display
if os was set to something, ping os wasn't loaded and we try to get overview graphs from it.

* Fix snmp_disable device page load error
When other os is set.

* Revamp os setting loading
the only safe way to access is Config::getOsSetting()

* Remove getOsSetting fallback behavior
Most instances don't use it and it can have unexpected results Config::getOsSetting('blah', 'group') == 'librenms'

* refactor and remove unneeded load_os/loadOs calls now since getOsSetting automatically loads it.

* restore unix overview graphs, they are different
small cleanups

* fix

app/Http/Controllers/Select/DeviceFieldController.php

@@ -82,7 +82,6 @@ class DeviceFieldController extends SelectController
 
         $text = $device[$field];
         if ($field == 'os') {
-            $device->loadOs();
             $text = Config::getOsSetting($text, 'text');
         } elseif ($field == 'type') {
             $text = ucfirst($text);