chore: 移除金币技能相关代码和配置

删除了SkillKind.Gold枚举、SkillConfig中的gold字段，移除了6303号金币技能配置，同时删除了施法系统中对应的金币添加逻辑

assets/script/game/hero/SCastSystem.ts

@@ -478,11 +478,6 @@ export class SCastSystem extends ecs.ComblockSystem implements ecs.ISystemUpdate
         } else if (kind === SkillKind.Shield && sAp !== 0) {
             const addShield = Math.max(0, Math.floor(sAp));
             model.add_shield(addShield);
-        } else if (kind === SkillKind.Gold) {
-            const addGold = config.gold ?? config.ap;
-            if (addGold > 0) {
-                MissionEconomy.addCoin(addGold);
-            }
         }
 
         if (config.buff_type !== undefined) {