LoW S3: adapt Urudin retreat AI to new Lua engine syntax

This is needed due to the recent refactor of the Lua AI engine in
commit f8f5557 (and related commits).

This fixes bug #24679.

data/campaigns/Legend_of_Wesmere/scenarios/chapter1/03_Kalian_under_Attack.cfg

@@ -39,16 +39,6 @@
         [/shift_labels]
     [/event]
 
-    [event]
-        name=preload
-        first_time_only=no
-        [lua]
-            code = <<
-				ai = {}
-			>>
-        [/lua]
-    [/event]
-
     {LOW_MASK 03_Kalian_under_Attack.mask (-7) (-7)}
     #### /Map setup ####
 
@@ -190,7 +180,6 @@
             [engine]
                 name=lua
                 code=<<
-				ai = ...
 				local my_ai = { }
 
 				function my_ai:retreat()