♻️ Remove unused return value from SpawnUnique

Introduced erroneously in f87bc0ca8b

Source/items.cpp

@@ -2667,10 +2667,10 @@ void GetUniqueItem(int i, int uid)
 	item[i]._iCreateInfo |= CF_UNIQUE;
 }
 
-int SpawnUnique(int uid, int x, int y)
+void SpawnUnique(int uid, int x, int y)
 {
 	if (numitems >= MAXITEMS)
-		return -1;
+		return;
 
 	int ii = AllocateItem();
 	GetSuperItemSpace(x, y, ii);
@@ -2684,7 +2684,7 @@ int SpawnUnique(int uid, int x, int y)
 	GetUniqueItem(ii, uid);
 	SetupItem(ii);
 
-	return ii;
+	return;
 }
 
 void ItemRndDur(int ii)

Source/items.h

@@ -49,7 +49,7 @@ void SaveItemPower(int i, int power, int param1, int param2, int minval, int max
 void GetItemPower(int i, int minlvl, int maxlvl, int flgs, BOOL onlygood);
 void SetupItem(int i);
 int RndItem(int m);
-int SpawnUnique(int uid, int x, int y);
+void SpawnUnique(int uid, int x, int y);
 void SpawnItem(int m, int x, int y, BOOL sendmsg);
 void CreateRndItem(int x, int y, BOOL onlygood, BOOL sendmsg, BOOL delta);
 void CreateRndUseful(int pnum, int x, int y, BOOL sendmsg);