DB/Naxxramas: Migrate linked_respawn to spawn groups

src/server/scripts/Northrend/Naxxramas/naxxramas.h

@@ -27,21 +27,21 @@ uint32 const EncounterCount     = 15;
 
 enum NAXEncounter
 {
-    BOSS_ANUBREKHAN,
-    BOSS_FAERLINA,
-    BOSS_MAEXXNA,
-    BOSS_NOTH,
-    BOSS_HEIGAN,
-    BOSS_LOATHEB,
-    BOSS_PATCHWERK,
-    BOSS_GROBBULUS,
-    BOSS_GLUTH,
-    BOSS_THADDIUS,
-    BOSS_RAZUVIOUS,
-    BOSS_GOTHIK,
-    BOSS_HORSEMEN,
-    BOSS_SAPPHIRON,
-    BOSS_KELTHUZAD
+    BOSS_ANUBREKHAN = 0,
+    BOSS_FAERLINA   = 1,
+    BOSS_MAEXXNA    = 2,
+    BOSS_NOTH       = 3,
+    BOSS_HEIGAN     = 4,
+    BOSS_LOATHEB    = 5,
+    BOSS_PATCHWERK  = 6,
+    BOSS_GROBBULUS  = 7,
+    BOSS_GLUTH      = 8,
+    BOSS_THADDIUS   = 9,
+    BOSS_RAZUVIOUS  = 10,
+    BOSS_GOTHIK     = 11,
+    BOSS_HORSEMEN   = 12,
+    BOSS_SAPPHIRON  = 13,
+    BOSS_KELTHUZAD  = 14
 };
 
 enum NAXData