Clean-up: remove dpi value from from xsettings-xml (MR 9)

The dpi value was implemented with the idea to make it overridable by
device package post-install scripts. This approach was wrong, as it's
not a clean way to override configs. Let's remove the dpi value again.

config/xfce4/xfconf/xfce-perchannel-xml/xsettings.xml

 <?xml version="1.0" encoding="UTF-8"?>
 
 <channel name="xsettings" version="1.0">
-  <property name="Xft" type="empty">
-    <property name="DPI" type="int" value="96"/>
-  </property>
   <property name="Net" type="empty">
     <property name="IconThemeName" type="string" value="Faenza-Ambiance"/>
   </property>