fix(DB/GameEvents): Great-Father Winter's Helper NPCs should be present only during Winter Veil: Gifts event. (#10064)

Fixes #9981

data/sql/updates/pending_db_world/rev_1641645833659060700.sql

@@ -0,0 +1,6 @@
+INSERT INTO `version_db_world` (`sql_rev`) VALUES ('1641645833659060700');
+
+DELETE FROM `game_event_creature` WHERE `guid` IN (3565,3566);
+INSERT INTO `game_event_creature` VALUES
+(52,3565),
+(52,3566);