Add type-hint to debug null value fatal error

- Part of https://github.com/friendica/friendica/issues/7675#issuecomment-566076500

src/App.php

@@ -383,7 +383,7 @@ class App
 	 * @deprecated 2019.09 - Use BaseURL->remove() instead
 	 * @see        BaseURL::remove()
 	 */
-	public function removeBaseURL($origURL)
+	public function removeBaseURL(string $origURL)
 	{
 		return $this->baseURL->remove($origURL);
 	}

src/Core/System.php

@@ -41,7 +41,7 @@ class System extends BaseObject
 	 * @return string The cleaned url
 	 * @throws \Exception
 	 */
-	public static function removedBaseUrl($orig_url)
+	public static function removedBaseUrl(string $orig_url)
 	{
 		return self::getApp()->removeBaseURL($orig_url);
 	}