small UtBS unit WML clean up (4 units)

This commit prepares for the animation WML overhaul on UtBS, but is
independant
* fixing comments for divine avatar, desert ranger
* deleting duplicate WML for dark assassin, corrupted elf

data/campaigns/Under_the_Burning_Suns/units/elves/Corrupted_Elf.cfg

@@ -12,7 +12,6 @@
     advances_to=null
     level=3
     alignment=chaotic
-    advances_to=null
     cost=100
     usage=fighter
     description= _ "Imbued with a dark spirit these corrupted elves combine unhuman strength with potent magics to create formidable opponents. Though the elvish body often decays quickly, these abominations are potent weapons of the undead lords."+{SPECIAL_NOTES}+{SPECIAL_NOTES_MAGICAL}

data/campaigns/Under_the_Burning_Suns/units/elves/Desert_Ranger.cfg

@@ -7,12 +7,12 @@
     {MAGENTA_IS_THE_TEAM_COLOR}
     hitpoints=42
     movement_type=desert_elf
-    # Avengers move faster in mountains and shallow water
+    # Rangers move faster in mountains and shallow water
     [movement_costs]
         shallow_water=2
         mountains=2
     [/movement_costs]
-    # Ranger defend better in shallow water and swamp
+    # Rangers defend better in shallow water and swamp
     [defense]
         shallow_water=70
         swamp_water=60

data/campaigns/Under_the_Burning_Suns/units/elves/Divine_Avatar.cfg

@@ -29,7 +29,7 @@
     [/attack]
     [attack]
         name=lightbeam
-        description= _"lightbeam"	# wmllint: no spellcheck (until nane->id)
+        description= _"lightbeam"	# wmllint: no spellcheck (until name->id)
         type=arcane
         range=ranged
         [specials]

data/campaigns/Under_the_Burning_Suns/units/orcs/Dark_Assassin1.cfg

@@ -21,20 +21,12 @@
     [defend]
         start_time=-150
         sound_start_time=-25
-
         [if]
             hits=hit
             [sound_frame]
                 sound={SOUND_LIST:ORC_SMALL_HIT}
-                duration=100
             [/sound_frame]
         [/if]
-        [else]
-            hits=miss,kill
-            [sound_frame]
-                duration=100
-            [/sound_frame]
-        [/else]
 
         [frame]
             image="units/orcs/nightblade-defend-se1-[1~5].png:100"