Use CallManager.getMute() in PhoneUtils.

Currently, PhoneUtils.getMute() only get mute state from the foreground phone.
But if the fg phone is idle while a bg phone is off-hook, then we should get
the mute state from the bg phone. All the logic should be done in
CallManager.getMute() so PhoneUtils just needs to call that.

Bug: 3323789
Change-Id: I21ad6df19aa82f720e746f8d3f6a4ba5933c639e
diff --git a/src/com/android/phone/PhoneUtils.java b/src/com/android/phone/PhoneUtils.java
index 126af4f..a06760e 100644
--- a/src/com/android/phone/PhoneUtils.java
+++ b/src/com/android/phone/PhoneUtils.java
@@ -1832,17 +1832,16 @@
      * foreground call
      */
     static boolean getMute() {
-        Phone phone = PhoneApp.getInstance().mCM.getFgPhone();
+        PhoneApp app = PhoneApp.getInstance();
 
-        Context context = phone.getContext();
         boolean routeToAudioManager =
-            context.getResources().getBoolean(R.bool.send_mic_mute_to_AudioManager);
+            app.getResources().getBoolean(R.bool.send_mic_mute_to_AudioManager);
         if (routeToAudioManager) {
             AudioManager audioManager =
-                (AudioManager) phone.getContext().getSystemService(Context.AUDIO_SERVICE);
+                (AudioManager) app.getSystemService(Context.AUDIO_SERVICE);
             return audioManager.isMicrophoneMute();
         } else {
-            return phone.getMute();
+            return app.mCM.getMute();
         }
     }