Don't output flags for "adv" library in wx-config

This allows to keep the existing makefiles or configure scripts for
building wxWidgets applications using wx-config unchanged to keep them
working with the existing wxWidgets releases without adding an
unnecessary dependency on the "adv" library when using the latest Git or
3.1.2, when it's released.

wx-config.in

@@ -1242,6 +1242,10 @@ else    # MONOLITHIC = 0
         fi
     fi
 
+    # Existing scripts may use "wx-config --libs std,adv" or similar, but "adv"
+    # library is not used any longer.
+    wx_libs=`remove_field adv $wx_libs`
+
     if [ -n "$output_option_libs" ]; then
         using_gui=no
         for i in $wx_libs ; do