Remove wtf if no display nits mapping exists

Devices without a backlight will not provide nits mappings via hardware
composer, which is perfectly normal and has no side effects.

Bug: 234889959
Change-Id: I7f5f0e4e24bfb38335dfe09102b36b106a904d2d

services/core/java/com/android/server/display/DisplayDeviceConfig.java

@@ -246,7 +246,6 @@ public class DisplayDeviceConfig {
      */
     public float getNitsFromBacklight(float backlight) {
         if (mBacklightToNitsSpline == null) {
-            Slog.wtf(TAG, "requesting nits when no mapping exists.");
             return NITS_INVALID;
         }
         backlight = Math.max(backlight, mBacklightMinimum);