Example: D8 - Remove a service definition. Put in src directory of a module.

myModuleServiceProvider.php

<?php

namespace Drupal\myModule;

use Drupal\Core\DependencyInjection\ContainerBuilder;
use Drupal\Core\DependencyInjection\ServiceProviderBase;

/**
 * Removes the internationalization service definitions from twig_extension.
 */
class myModuleServiceProvider extends ServiceProviderBase {

  /**
   * {@inheritdoc}
   */
  public function alter(ContainerBuilder $container) {
    $container->removeDefinition('twig_extensions.twig.i18n');
    $container->removeDefinition('twig_extensions.twig.intl');
  }
}