Only show the schedule text for the night display and dark theme

In Android S design, night display and dark theme only show
schedule text for summary.

- Rmove redundant string resource.
- Remove redundant method in night display formatter.
- Refactor the code in dark mode preference and night display
controller.

Test: See the correct behavior in screen.
Fix: 174964139
Change-Id: I658b3073a0a6ed83f589103999c711e5430eaeb7

src/com/android/settings/display/NightDisplayTimeFormatter.java

@@ -17,8 +17,8 @@
 package com.android.settings.display;
 
 import android.content.Context;
-
 import android.hardware.display.ColorDisplayManager;
+
 import com.android.settings.R;
 
 import java.text.DateFormat;
@@ -45,13 +45,6 @@ public class NightDisplayTimeFormatter {
         return mTimeFormatter.format(c.getTime());
     }
 
-    public String getAutoModeTimeSummary(Context context, ColorDisplayManager manager) {
-        final int summaryFormatResId =
-                manager.isNightDisplayActivated() ? R.string.night_display_summary_on
-                        : R.string.night_display_summary_off;
-        return context.getString(summaryFormatResId, getAutoModeSummary(context, manager));
-    }
-
     public String getAutoModeSummary(Context context, ColorDisplayManager manager) {
         final boolean isActivated = manager.isNightDisplayActivated();
         final int autoMode = manager.getNightDisplayAutoMode();