Not much time after I installed my ubuntu, I installed ubuntu tweak and added shortcut keys for the applications I used most.
However, I wanted to remove a shortcut key and was not able to (the last one). At least, I couldn't figure out a way to do that. I want to reconfigure them using ubuntu's keyboard tool, so I don't mind if I have to delete all shortcut keys from ubuntu tweak. Does anyone know how to do that?
Double-click the command to display the window shown.
Then press ESC i.e. the escape key and the key will be removed that is displayed as disabled
That just leaves the Command itself. Double click the Command to edit and type None. Press Enter and the Command will be removed.
If using Escape doesn't work, follow most of the steps by fossfreedom but when you get to the part where you would press Escape, instead press Backspace and that should delete the command/key binding.
Keep in mind though, when you move to the keyboard shortcut system that Ubuntu provides by default, you will not be allowed to use the "Super" key in your shortcut...for some reason it is disabled there. You can apply it as a shortcut but the shortcut will never work unless used via Ubuntu Tweak or CCSM (Compiz).
The "Mod2" key that keep turn ON is actually the Num Lock key (...), as ridiculous as it may seems.
Turn Num Lock off, then press Backspace. The shortcut will (finally) be deleted. This also work on Ubuntu 12.04.