Date Format dialog flashes up when file/properties used

When you select the File/Properties dialog, in the construction of that
a 'Date Format' dialog flashes up while the date component is moved to
the properties dialog. Can mainly be seen on Windows so remove the
visible setting in glade file.

gnucash/gtkbuilder/gnc-date-format.glade

@@ -35,7 +35,6 @@
     </data>
   </object>
   <object class="GtkWindow" id="gnc_date_format_window">
-    <property name="visible">True</property>
     <property name="can_focus">False</property>
     <property name="title" translatable="yes">Date Format</property>
     <property name="resizable">False</property>