How to remove the deprecation warnings in Symfony 2.7?

Question

The dreaded "is deprecated since version 2.6 and will be removed in 3.0" errors that Symfony is outputting all over the logs and console. I've followed all the guidelines I found that claim to solve it, including upgrading sensio/distribution-bundle and putting ~E_USER_DEPRECATED into php.ini

Still getting these messages spammed over me. Aside from some hard measures like forking Symfony or overwriting the trigger_error function, what am I missing?

php.ini:

error_reporting = E_ALL & ~E_DEPRECATED & ~E_STRICT

bootstrap.php.cache:

namespace {
    error_reporting(error_reporting() & ~E_USER_DEPRECATED);
    $loader = require_once __DIR__.'/./autoload.php';
}