Remove unneeded var assignment

The $id variable is assigned, but never used in the script. This may
confuse readers, so remove the assignment.

Signed-off-by: Floris Luiten <floris.luiten@tweakers.net>

examples/signon.php

@@ -32,7 +32,6 @@ if (isset($_POST['user'])) {
     /* Update another field of server configuration */
     $_SESSION['PMA_single_signon_cfgupdate'] = ['verbose' => 'Signon test'];
     $_SESSION['PMA_single_signon_HMAC_secret'] = hash('sha1', uniqid(strval(random_int(0, mt_getrandmax())), true));
-    $id = session_id();
     /* Close that session */
     @session_write_close();
     /* Redirect to phpMyAdmin (should use absolute URL here!) */