remove dead panel version of the master volume pulldown.

the floater version turned out easier to get on-spec (though not perfect).

indra/newview/skins/default/xui/en/panel_volume_pulldown.xml

@@ -1,32 +0,0 @@
-<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
-<panel
-   chrome="true"
-   border="false"
-   follows="all"
-   height="50"
-   label="xSounds"
-   layout="topleft"
-   left="1"
-   name="xPreference Media panel"
-   top="1"
-   width="150">
-    <slider
-     control_name="AudioLevelMaster"
-     follows="left|top"
-     font.style="BOLD"
-     height="15"
-     increment="0.05"
-     initial_value="0.5"
-     layout="topleft"
-     left="0"
-     name="System Volume"
-     show_text="false"
-     slider_label.halign="right"
-     top_pad="5"
-     volume="true"
-     width="120">
-        <slider.commit_callback
-         function="Vol.setControlFalse"
-         parameter="MuteAudio" />
-    </slider>
-</panel>