uninstall.php

<?php 

// Delete media files directory
$mediaPath = rex_path::addonData('feeds', 'media');
if (is_dir($mediaPath)) {
    $files = glob($mediaPath . '/*');
    foreach($files as $file) {
        if(is_file($file)) {
            unlink($file);
        }
    }
    rmdir($mediaPath);
}

// delete ForeignKey
rex_sql_table::get(rex::getTable('feeds_stream'))
->removeForeignKey('rex_feeds_item_ibfk_1')
->ensure();  

# delete media effect
$sql = rex_sql::factory();
$sql->setTable(rex::getTablePrefix().'media_manager_type');
$sql->setWhere(['name'=>'feeds_thumb']);
$sql->delete();

$sql->setTable(rex::getTablePrefix().'media_manager_type_effect');
$sql->setWhere(['createuser'=>'feeds']);
$sql->delete();

// delete tables
$sql->setQuery(sprintf('DROP TABLE IF EXISTS `%s`;', rex::getTable('feeds_item')));
$sql->setQuery(sprintf('DROP TABLE IF EXISTS `%s`;', rex::getTable('feeds_stream')));