Removed setting override system due to confusing behaviour

- Was only used to disable registration when LDAP was enabled.
- Caused saved option not to show on settings page causing confusion.
- Extended setting logic where used to take ldap into account instead of
global override.
- Added warning on setting page to show registration enable setting is
not used while ldap is active.

For #1541

app/Settings/SettingService.php

@@ -98,12 +98,6 @@ class SettingService
      */
     protected function getValueFromStore($key, $default)
     {
-        // Check for an overriding value
-        $overrideValue = $this->getOverrideValue($key);
-        if ($overrideValue !== null) {
-            return $overrideValue;
-        }
-
         // Check the cache
         $cacheKey = $this->cachePrefix . $key;
         $cacheVal = $this->cache->get($cacheKey, null);
@@ -255,20 +249,4 @@ class SettingService
     {
         return $this->setting->where('setting_key', '=', $key)->first();
     }
-
-
-    /**
-     * Returns an override value for a setting based on certain app conditions.
-     * Used where certain configuration options overrule others.
-     * Returns null if no override value is available.
-     * @param $key
-     * @return bool|null
-     */
-    protected function getOverrideValue($key)
-    {
-        if ($key === 'registration-enabled' && config('auth.method') === 'ldap') {
-            return false;
-        }
-        return null;
-    }
 }