I am not seeing this $modSettings['force_ssl'] variable defined any where in the codebase except this one spot
In sources/Load.php
if (!empty($modSettings['force_ssl']) && $image_proxy_enabled && stripos($user_settings['avatar'], 'http://') !== false)
$user_settings['avatar'] = strtr($boardurl, array('http://' => 'https://')) . '/proxy.php?request=' . urlencode($user_settings['avatar']) . '&hash=' . md5($user_settings['avatar'] . $image_proxy_secret);
Possibly leftover code while porting from 2.1.
Correct... it doesn't belong there...
This was fixed in 2.0.15.