Use Slog.e() instead of Slog.wtf() for unknown restrictions

Slog.wtf() normally indicates a bug in the system, but in this case
it's a caller side issue, so e() is more suitable.

Bug 26918715

Change-Id: I94980cb9dafd34e6c5672bf833fec921df14e6a1

services/core/java/com/android/server/pm/UserRestrictionsUtils.java

@@ -155,7 +155,7 @@ public class UserRestrictionsUtils {
      */
     public static boolean isValidRestriction(@NonNull String restriction) {
         if (!USER_RESTRICTIONS.contains(restriction)) {
-            Slog.wtf(TAG, "Unknown restriction: " + restriction);
+            Slog.e(TAG, "Unknown restriction: " + restriction);
             return false;
         }
         return true;