[i18n] Minor cleanup in Slovak (#2502)

Follow-up to <https://github.com/FreshRSS/FreshRSS/pull/2500>. The languages aren't translated, so they don't need to be there.

app/i18n/en/gen.php

@@ -127,6 +127,7 @@ return array(
 		'oc' => 'Occitan',
 		'pt-br' => 'Português (Brasil)',
 		'ru' => 'Русский',
+		'sk' => 'Slovenčina',
 		'tr' => 'Türkçe',
 		'zh-cn' => '简体中文',
 	),

app/i18n/sk/gen.php

@@ -114,23 +114,6 @@ return array(
 		'new_article' => 'Našli sa nové články. Kliknite na obnovenie stránky.',
 		'should_be_activated' => 'Musíte povoliť JavaScript',
 	),
-	'lang' => array(
-		'cz' => 'Čeština',
-    'sk' => 'Slovenčina',
-		'de' => 'Deutsch',
-		'en' => 'English',
-		'es' => 'Español',
-		'fr' => 'Français',
-		'he' => 'עברית',
-		'it' => 'Italiano',
-		'kr' => '한국어',
-		'nl' => 'Nederlands',
-		'oc' => 'Occitan',
-		'pt-br' => 'Português (Brasil)',
-		'ru' => 'Русский',
-		'tr' => 'Türkçe',
-		'zh-cn' => '简体中文',
-	),
 	'menu' => array(
 		'about' => 'O FreshRSS',
 		'admin' => 'Administrácia',