fix(VDialog): remove aria-expanded from activator

[paul-thebaud]

Description

Remove useless aria-expanded attribute on dialog activators to follow WAI-ARIA recommandations.

When focusing a dialog activator, dialog will never already be expanded, so this information is useless and will pollute screen readers users.

Markup:

<template>
<v-app>
  <v-container>
    <v-dialog>
      <template #activator={ props }>
        <v-btn v-bind="props">Open</v-btn>
      </template> 
    </v-dialog>
  </v-container>
</v-app>
</template>