fix(hero prefab & gui): 调整多个英雄预制体和阴影UI的位置参数

1. 修正mb1到mb6共6个英雄预制体的节点Y轴偏移与坐标数值
2. 精简shadow.prefab的冗余节点组件，调整缩放、尺寸和填充模式参数

assets/resources/game/heros/mb2.prefab

@@ -167,7 +167,7 @@
     "value": {
       "__type__": "cc.Vec3",
       "x": 0,
-      "y": 5,
+      "y": 2.253,
       "z": 0
     }
   },
@@ -212,8 +212,8 @@
     ],
     "value": {
       "__type__": "cc.Vec3",
-      "x": 0.25,
-      "y": 0.7,
+      "x": 2,
+      "y": 2,
       "z": 1
     }
   },