Cleanup gnome-themes from old stock icons

[Luca Ferretti <elle uca libero it>]

There are a lot of old and now unused icons in gnome-themes, for
example:

./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_panel_hide_up.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_panel_hide_right.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_panel_hide_left.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_panel_hide_down.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_panel_hide_up.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_panel_hide_right.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_panel_hide_left.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_panel_hide_down.png
./gtk-themes/LargePrint/pixmaps/stock_panel_hide_up.png
./gtk-themes/LargePrint/pixmaps/stock_panel_hide_right.png
./gtk-themes/LargePrint/pixmaps/stock_panel_hide_left.png
./gtk-themes/LargePrint/pixmaps/stock_panel_hide_down.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_panel_hide_up.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_panel_hide_right.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_panel_hide_left.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_panel_hide_down.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_menu-panel.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_sliding-panel.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_floating-panel.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_edge-panel.png
./gtk-themes/HighContrastLargePrintInverse/pixmaps/stock_corner-panel.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_menu-panel.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_sliding-panel.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_floating-panel.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_edge-panel.png
./gtk-themes/HighContrastLargePrint/pixmaps/stock_corner-panel.png
./gtk-themes/LargePrint/pixmaps/stock_menu-panel.png
./gtk-themes/LargePrint/pixmaps/stock_sliding-panel.png
./gtk-themes/LargePrint/pixmaps/stock_floating-panel.png
./gtk-themes/LargePrint/pixmaps/stock_edge-panel.png
./gtk-themes/LargePrint/pixmaps/stock_corner-panel.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_menu-panel.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_sliding-panel.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_floating-panel.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_edge-panel.png
./gtk-themes/LowContrastLargePrint/pixmaps/stock_corner-panel.png

OK to delete them and remove from panel-stock-icons.rc?

Of course there are also other old icons to remove, I'll report (and
remove, if it's OK for module maintainer) after checking in
panel-stock-icons.h