Address PHPStan warnings in 'classes/db.php'.

------ --------------------------------------------------
Line   classes/db.php
------ --------------------------------------------------
7      Property Db::$link is unused.
86     Property Db::pdo (PDO) in empty() is not falsy.
------ --------------------------------------------------

1 files changed, 1 insertions, 3 deletions

diff --git a/classes/db.php b/classes/db.php
index a09c44628..7b669cf32 100755
--- a/classes/db.php
+++ b/classes/db.php
@@ -4,9 +4,7 @@ class Db
 	/** @var Db $instance */
 	private static $instance;
 
-	private $link;
-
-	/** @var PDO $pdo */
+	/** @var PDO|null $pdo */
 	private $pdo;
 
 	function __construct() {