Use UM.DISALLOW_OEM_UNLOCK instead of Global.OEM_UNLOCK_DISALLOWED

Currently we used global setting to restrict user from enabling oem
unlock. As global settings can be chagned using adb, using user
restrictions instead.

Bug: 29893399
Change-Id: I3eab3b323ed3d1da7fcf3b26560a6fa04ec0f1f9
diff --git a/Settings/src/com/android/tv/settings/system/development/DevelopmentFragment.java b/Settings/src/com/android/tv/settings/system/development/DevelopmentFragment.java
index 40e577e..d119a65 100644
--- a/Settings/src/com/android/tv/settings/system/development/DevelopmentFragment.java
+++ b/Settings/src/com/android/tv/settings/system/development/DevelopmentFragment.java
@@ -843,8 +843,7 @@
     }
 
     private boolean isOemUnlockAllowed() {
-        return Settings.Global.getInt(getActivity().getContentResolver(),
-                Settings.Global.OEM_UNLOCK_DISALLOWED, 0) == 0;
+        return !mUm.hasUserRestriction(UserManager.DISALLOW_OEM_UNLOCK);
     }
 
     private void updateBugreportOptions() {