places view: Remvoe some unused style classes

These style classes were not used in Adwaita, and didn't make
any difference for the appearance.

gtk/ui/gtkplacesview.ui

@@ -134,9 +134,6 @@
                         <signal name="row-activated" handler="on_listbox_row_activated" object="GtkPlacesView" swapped="yes"/>
                       </object>
                     </child>
-                    <style>
-                      <class name="view"/>
-                    </style>
                   </object>
                 </child>
               </object>

gtk/ui/gtkplacesviewrow.ui

@@ -5,9 +5,6 @@
     <property name="width_request">100</property>
     <property name="visible">True</property>
     <property name="can_focus">True</property>
-    <style>
-      <class name="volume-row"/>
-    </style>
     <child>
       <object class="GtkEventBox" id="event_box">
         <property name="visible">1</property>