Remove mysqli_close from clean_table.inc

Backported from master. See https://github.com/php/php-src/pull/8427

ext/mysqli/tests/clean_table.inc

@@ -8,7 +8,4 @@ if (!$link = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket)) {
 
 if (!mysqli_query($link, 'DROP TABLE IF EXISTS test')) {
     printf("[clean] Failed to drop old test table: [%d] %s\n", mysqli_errno($link), mysqli_error($link));
-}
-
-mysqli_close($link);
-?>
+}