docs(input): remove tabindex from example (#9111)

Author: Hirse

src/material-examples/dialog-overview/dialog-overview-example-dialog.html

@@ -2,7 +2,7 @@ <h1 mat-dialog-title>Hi {{data.name}}</h1>
 <div mat-dialog-content>
   <p>What's your favorite animal?</p>
   <mat-form-field>
-    <input matInput tabindex="1" [(ngModel)]="data.animal">
+    <input matInput [(ngModel)]="data.animal">
   </mat-form-field>
 </div>
 <div mat-dialog-actions>