As it turns out, the settings have never had any effect on file uploads since version 5.0.
The reason is that this setting, as well as upload_max_size act upon data in $_POST and $_FILES. As it turns out, since the REST API uses the request body to transport binary file data, it by passes this check. Quoting the PHP doc: "If the size of post data is greater than post_max_size, the $_POST and $_FILES superglobals are empty."
Given that we do not say anywhere that we "support" this setting, I'm not sure we should remove it. The size of the files can still be validated using the size configuration of the Field Definition. From a user's perspective, it's actually simpler.
Note however that it will affect file upload done via symfony forms when implemented, since those will use standard POST and multipart form-data.
When it comes to limiting the size of requests sent altogether to the server, there are directives for this in our example / template web server configuration files: https://github.com/ezsystems/ezplatform/blob/master/doc/apache2/vhost.template#L14, https://github.com/ezsystems/ezplatform/blob/master/doc/nginx/vhost.template#L21.
I'm tempted to disqualify the issue (e.g. "you don't qualify as an issue" ).