Fix Respecc token not working at most rogue trainers.

[Saltgurka]

• Caused by core script npc_rogue_trainer overwriting the gossip menu.
• Moved the letter gossip option to now be available globally for all rogue trainers instead of in a npcs_special script
• Resolves: https://github.com/Looking4Group/L4G_Core/issues/3807
• Requires the following DB queries to be run:

UPDATE `creature_template` SET `ScriptName`='' WHERE `ScriptName`='npc_rogue_trainer';

DELETE FROM `npc_option` WHERE `id`=54;
INSERT INTO `npc_option` (`id`, `npcflag`, `action`, `option_text`) VALUES
('54', '16', '21', '<Take the letter>');