Remove brightness-switch properties from configs (MR 8)

When removed, default settings will be used.

config/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml

@@ -2,8 +2,6 @@
 
 <channel name="xfce4-power-manager" version="1.0">
   <property name="xfce4-power-manager" type="empty">
-    <property name="brightness-switch-restore-on-exit" type="int" value="-1"/>
-    <property name="brightness-switch" type="int" value="0"/>
     <property name="show-tray-icon" type="bool" value="false"/>
     <property name="show-panel-label" type="int" value="1"/>
   </property>