Lichform can not be unlearnt

git-svn-id: http://svn.net-core.org/repos/t-engine4@4745 51575b47-30f0-44d4-a5cc-537603b46e54

game/modules/tome/data/talents/spells/necrosis.lua

@@ -141,6 +141,7 @@ newTalent{
 	points = 5,
 	sustain_mana = 150,
 	cooldown = 30,
+	no_unlearn_last = true,
 	no_npc_use = true,
 	becomeLich = function(self, t)
 		self.descriptor.race = "Undead"