THoT S12 Fix some "x=" tests that should be "x,y=" tests

Taking the chest south of the start hid the door and chest that are
north of the start.

The sneak-door opened much earlier in the level, allowing the undead
from the south-east lich to go north to the spider room.  The ghosts
and nightstalkers that are supposed to ambush the player's forces in
the south (after opening the 3-hex door) instead go north and end up
joining the spider fight.  The slower-moving undead also go north,
and are easily fought one-by-one in the sneak passage instead of the
south-east.

data/campaigns/The_Hammer_of_Thursagan/scenarios/12_The_Underlevels.cfg

@@ -800,7 +800,7 @@
         [/gold]
 
         [remove_item]
-            x=15,38
+            x,y=15,38
         [/remove_item]
     [/event]
 
@@ -827,7 +827,7 @@
         name=moveto
         [filter]
             side=1
-            x=55,33
+            x,y=55,33
         [/filter]
 
         [message]