Removed the hard-coded MySQL default port and the usage of ini-settings

[morozov]

Q	A
Type	improvement
BC Break	no

There's no need to use the hard-coded MySQL port 3306 in the DBALs codebase. There's also no need to manually pass the value obtainer from ini_get('mysqli.default_port') to the driver. The driver doesn't require a port and is aware of the default port:

<?php declare(strict_types=1);

$conn = mysqli_init();
$conn->real_connect('localhost', 'root');
var_dump($conn->query('SELECT VERSION()')->fetch_row());

/*array(1) {
  [0] =>
  string(6) "5.7.27"
}*/