Revert "Avoid [+campaign] use"

This reverts commit f29ff05. Since ENABLE_KRAKEN is defined in one of
the DW unit files, this causes the preprocessor to fail on game start.

data/campaigns/Dead_Water/_main.cfg

@@ -20,8 +20,6 @@
     {CAMPAIGN_DIFFICULTY HARD      "units/merfolk/warrior.png~RC(magenta>red)" ( _ "Warrior") ( _ "Challenging")}
     {CAMPAIGN_DIFFICULTY NIGHTMARE "units/merfolk/triton.png~RC(magenta>red)" ( _ "Triton") ( _ "Difficult")}
 
-    {ENABLE_KRAKEN}
-
     description= _ "You are Kai Krellis, son and heir of the last merman king but only a child. A necromancer is turning your subjects into undead slaves! Lead your people on a mission to convince a powerful mer-sorceress to help you repel the invasion. The oceans near the Northern Lands are perilous, so you will need cunning and bravery to survive. But first you need to gain the respect of your troops!
 
 " + _ "(Intermediate level, 10 scenarios.)"
@@ -73,6 +71,13 @@
     {campaigns/Dead_Water/units}
 [/units]
 
+# wmllint bug: wmllint is not smart enough to realise that the campaign already has an id
+# wmllint: validate-off
+[+campaign]
+    {ENABLE_KRAKEN}
+[/campaign]
+# wmllint: validate-on
+
 {campaigns/Dead_Water/scenarios}
 
 [lua]