fix(ui/homepage/设备说明): 调整布局底部边距，移除冗余的Start初始化调用

1.  调整了首页设备说明预制体的m_Bottom布局边距从0改为30，修复布局偏移问题
2.  移除了DeviceTeachingPage中冗余的自动调用Init的Start方法

Assets/Res/ui/homepage/消息详情.prefab

@@ -240,7 +240,7 @@ MonoBehaviour:
     m_Left: 0
     m_Right: 0
     m_Top: 0
-    m_Bottom: 0
+    m_Bottom: 30
   m_ChildAlignment: 1
   m_Spacing: 45
   m_ChildForceExpandWidth: 1

Assets/Scripts/UI/Pages/SelfPage/DeviceTeachingPage.cs

@@ -13,9 +13,6 @@ namespace Kill.UI.Pages
         public GameObject videoPlane;
         public VideoCtrl videoCtrl;
         public List<DeviceTeachingVideo> deviceTeachingVideos;
-        private void Start() {
-            Init(null);
-        }
         public void Init(Action callback)
         {
             this.callback=callback;