Prose: the Storm Trident's description uses "merfolk" (issue #2936)

Also update Dead Water's copy of it to use race= instead of a
list of unit types (as done for the core object in 613dd43).

(cherry-picked from commit ad7bc19)

data/campaigns/Dead_Water/utils/items.cfg

@@ -1,18 +1,18 @@
 #textdomain wesnoth-dw
 
-# This copy of OBJ_TRIDENT_STORM adds the new merman types to the allowed units, and is only the object. It doesn't include the event for picking it up. The trident in wolf_coast uses a more complicated event for picking it up.
+# This copy of OBJ_TRIDENT_STORM is only the object, it doesn't include the event for picking it up. This trident is used in the wolf_coast scenario, which uses a campaign-specific set of events for picking it up.
 
 #define STORM_TRIDENT X Y ID
     [object]
         id={ID}
         name= _ "Storm Trident"
         image=items/storm-trident.png
         duration=forever
-        description= _ "This weapon shoots powerful lightning bolts at your enemies."
+        description= _ "This trident gives merfolk the power to throw lightning at their enemies."
         silent=yes
-        cannot_use_message= _ "Only a merman can use this item."
+        cannot_use_message= _ "Only the merfolk can use this item."
         [filter]
-            type=Merman Citizen,Merman Brawler,Merman Child King,Merman Young King,Merman Soldier King,Merman Warrior King,Mermaid Diviner,Mermaid Enchantress,Mermaid Initiate,Mermaid Priestess,Mermaid Siren,Merman Entangler,Merman Fighter,Merman Hoplite,Merman Hunter,Merman Javelineer,Merman Netcaster,Merman Spearman,Merman Triton,Merman Warrior
+            race=merman
             x={X}
             y={Y}
         [/filter]

data/core/macros/items.cfg

@@ -518,7 +518,7 @@
             name= _ "Storm Trident"
             image=items/storm-trident.png
             duration=forever
-            description= _ "This trident allows a merman to shoot electric bolts at his enemies!"
+            description= _ "This trident gives merfolk the power to throw lightning at their enemies."
             [effect]
                 apply_to=new_attack
                 name="storm trident"