Button mapping contains GUI buttons as well

<Build: UME Daily 20080506 Mccaslin, UME Beta 4 Menlow>
<Environment: Q1 and Jax10>

Summary:
The button mapping utility in Preferences seems to list GUI buttons for mapping as well. I do not believe we should let the user see these options. Only hardware buttons should be available for mapping.

Steps to Reproduce:
1) Navigate to Preferences screen
2) Select Buttons applet
3) Use arrow to scroll to bottom of list

Expected result:
Only actions with hardware buttons mapped are shown

Actual result:
List contains what looks like software button listings as well:
XF86AudioMute
XF86AudioPause