Delete unused "File observer" notification channel

Signed-off-by: AJ Jordan <alex@strugee.net>

src/main/java/com/owncloud/android/MainApp.java

@@ -500,9 +500,7 @@ public class MainApp extends MultiDexApplication implements HasAndroidInjector {
                               R.string.notification_channel_file_sync_name,
                               R.string.notification_channel_file_sync_description, context);
 
-                createChannel(notificationManager, NotificationUtils.NOTIFICATION_CHANNEL_FILE_OBSERVER,
-                              R.string.notification_channel_file_observer_name, R.string
-                                  .notification_channel_file_observer_description, context);
+                notificationManager.deleteNotificationChannel(NotificationUtils.NOTIFICATION_CHANNEL_FILE_OBSERVER);
 
                 createChannel(notificationManager, NotificationUtils.NOTIFICATION_CHANNEL_PUSH,
                               R.string.notification_channel_push_name, R.string

src/main/res/values/strings.xml

@@ -668,8 +668,6 @@
     <string name="notification_channel_media_description">Music player progress</string>
     <string name="notification_channel_file_sync_name">File sync</string>
     <string name="notification_channel_file_sync_description">Shows file sync progress and results</string>
-    <string name="notification_channel_file_observer_name">File observer</string>
-    <string name="notification_channel_file_observer_description">Monitors files for changes</string>
 
     <string name="account_not_found">Account not found!</string>