chore(demo): update to recommend pattern

Author: rdlabo

demo/src/app/index/pages/accordion/accordion.page.html

@@ -1,8 +1,6 @@
 <ion-header [translucent]="true">
   <ion-toolbar color="light">
-    <ion-buttons slot="start">
-      <ion-back-button defaultHref="/main/index"></ion-back-button>
-    </ion-buttons>
+    <ion-back-button slot="start" defaultHref="/main/index"></ion-back-button>
     <ion-title>accordion</ion-title>
   </ion-toolbar>
 </ion-header>