As the filter occurs within a class you must remove it by replacing $this (as you don’t run the remove_filter on the class, $this is not available) with the name of the class where it is declared.
An example with a class called : Wecba, you will remove it like this :
remove_filter('the_content', array('Wecba', 'add_Content_Ads'), 8);
It’s nos only depends on the class name.
Hope it helps