[securemail] Upgrade singpolyma/openpgp to version 0.6.0

- Add missing use statement in SecureTestEmail
- Address https://github.com/friendica/friendica/issues/12011#issuecomment-1321196332
- phpseclib version 3 dependency is implied from the core so it is removed from the addon

securemail/vendor/composer/autoload_static.php

@@ -11,17 +11,9 @@ class ComposerStaticInitSecuremailAddon
     );
 
     public static $prefixLengthsPsr4 = array (
-        'p' => 
-        array (
-            'phpseclib\\' => 10,
-        ),
     );
 
     public static $prefixDirsPsr4 = array (
-        'phpseclib\\' => 
-        array (
-            0 => __DIR__ . '/..' . '/phpseclib/phpseclib/phpseclib',
-        ),
     );
 
     public static $classMap = array (