upgrade ICU_DATA_VERSION to 50

in ICU_DATA_VERSION 49
```php

use Symfony\Component\Locale\Locale;

(count(Locale::getDisplayCountries('de')) != count(Locale::getDisplayCountries('en')))
/* 255 != 259 */
```

in ICU_DATA_VERSION 50
```php
/* 258 == 258 */
```

changelog:

- `const ICU_DATA_VERSION = '50';` in Locale class
- removed `Resources/data/49`
- added 50 version reference in `Resources/data/icu.ini`
- ran `php Resources/data/build-data.php 50` (!?!got parse errors!?!)