Rename settings category.

- from night light to night display.

Change-Id: I2d6c8d931793439dc3b028b4b7a46c21444e10a0
Fixes: 79530682
Test: make RunSettingsRoboTests

tests/robotests/src/com/android/settings/display/NightDisplaySettingsTest.java

@@ -48,8 +48,8 @@ public class NightDisplaySettingsTest {
     }
 
     @Test
-    public void getCategoryKey_isCategoryNightLight() {
+    public void getCategoryKey_isCategoryNightDisplay() {
         NightDisplaySettings settings = new NightDisplaySettings();
-        assertThat(settings.getCategoryKey()).isEqualTo(CategoryKey.CATEGORY_NIGHT_LIGHT);
+        assertThat(settings.getCategoryKey()).isEqualTo(CategoryKey.CATEGORY_NIGHT_DISPLAY);
     }
 }