Remove unused variables

src/Encrypt/Openssl.php

@@ -416,7 +416,7 @@ public function decrypt($value)
             throw new Exception\RuntimeException('Please give an envelope key for decryption with Openssl');
         }
 
-        foreach ($this->keys['private'] as $key => $cert) {
+        foreach ($this->keys['private'] as $cert) {
             $keys = openssl_pkey_get_private($cert, $this->getPassphrase());
         }