To disable a race from being playable, edit 'ChrRaces.dbc' and set the first column to 0.
Disabling a race's icon to be grayed out, edit 'CharBaseInfo.dbc'.
Simply go down to the race ID and remove it from all classes. It goes by 'raceID, classID'.
To completely take out the race icons themselves from the Character Creation screen, (I think editing ChrRaces.dbc should do that, but I'm not sure, so keep reading...), you'd need to go into your patch files to the following path: InterfaceGlueXMLCharacterCreate.xml.
Within that file, you can remove where the icons are at.
I'm not on my home PC, I can't see the files atm to tell you exactly how it would look like and what exactly to edit.
When I come back home, I'll edit this post with more information.