Unregister MobileNetworkRepository during onPause()

- Move MobileNetworkRepository unregistration from onDestory() to onPause() for corresponding to its registration by onResume.

Bug: 275456375
Test: built pass and verified in bug
Change-Id: I4cd2f23501485d4f3cfcf867cdb8d81e0385794a

src/com/android/settings/network/telephony/MobileNetworkSettings.java

@@ -350,10 +350,15 @@ public class MobileNetworkSettings extends AbstractMobileNetworkSettings impleme
         }
     }
 
+    @Override
+    public void onPause() {
+        mMobileNetworkRepository.removeRegister(this);
+        super.onPause();
+    }
+
     @Override
     public void onDestroy() {
         super.onDestroy();
-        mMobileNetworkRepository.removeRegister(this);
     }
 
     @VisibleForTesting