Singleton Class Unhook action and Filters

removeSingleton.php

class myClass{
	protected static $instance = null;
	
	public function __construct(){

		add_filter('the_content', array($this, 'add_text'));
	}
	
	public static function get_instance(){
		// If the single instance hasn't been set, set it now.
		if ( is_null( self::$instance ) ) {
			self::$instance = new self();
		}
		return self::$instance;
	}

	public function add_text($content){
		return 'digthis 123'.$content;
	}
}
add_action('init', array('myClass','get_instance'), 10);
add_action('init', function(){
	$pinstance = myClass::get_instance();
	remove_filter( 'the_content', array($pinstance,'add_text'), 10 );
}, 20);