Update description for wallpaper accessibility announcement string

    <!-- Accessibility string used as a label for a particular wallpaper in the Wallpaper Picker list.

         e.g. "Wallpaper 3 of 10" -->

    <string name="wallpaper_accessibility_name">Wallpaper %1$d of %2$d</string>

    <!-- Accessibility string used to announce that an item has been selected. -->

    <!-- Accessibility string used to announce that a wallpaper has been selected. -->

    <string name="announce_selection">Selected <xliff:g id="label" example="Wallpaper 3 of 10">%1$s</xliff:g></string>

    <!-- Label on button to delete wallpaper(s) -->