fix(flutter): 回退底部导航为四槽

lib/pages/discover/discover_view.dart

@@ -340,10 +340,6 @@ class _DiscoverPageState extends State<DiscoverPage> {
   }
 
   Widget _bottomNav(AppLocalizations l10n) => AppBottomNav(
-    centerAction: AppBottomNavCenterAction(
-      label: l10n.createTab,
-      onTap: () => _act(DiscoverPageAction.create),
-    ),
     items: [
       AppBottomNavItem(
         tabKey: const Key('discover-nav-home'),

lib/pages/home/home_view.dart

@@ -195,10 +195,6 @@ class _HomeTabsState extends State<_HomeTabs> {
   Widget _nav(BuildContext context, AppLocalizations l10n) {
     return AppBottomNav(
       barKey: const Key('home-tabs-bar'),
-      centerAction: AppBottomNavCenterAction(
-        label: l10n.createTab,
-        onTap: () => _selectTab(context, 2),
-      ),
       items: [
         _navItem(context, l10n, 0),
         _navItem(context, l10n, 1),

lib/pages/mine/mine_view.dart

@@ -242,10 +242,6 @@ class _MyPageState extends State<MyPage> {
 
   Widget _bottomNav(AppLocalizations l10n) {
     return AppBottomNav(
-      centerAction: AppBottomNavCenterAction(
-        label: l10n.createTab,
-        onTap: () => _act(MyPageAction.create),
-      ),
       items: [
         AppBottomNavItem(
           tabKey: const Key('mine-nav-home'),