jtag/aice/aice_usb: remove unused constants

Those are breaking the build with clang 3.4 (current default compiler
on OS X 10.9.2).

Change-Id: I9f2fbfbb6d544498cb8d6a62565e4ebe7223e784
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2077


Tested-by: jenkins
Reviewed-by: Hsiangkai Wang <hsiangkai@gmail.com>