xinput-calibrator: disable gtk gui explicitly

* if gtk is autodetected then gtkmm, glibmm, libcairomm-1.0-1,
  libpangomm-1.4-1, libsigc-2.0-0 are pulled to image like here:
  http://git.shr-project.org/git/?p=buildhistory.git;a=blobdiff;f=images/crespo/eglibc/shr-image/installed-package-names.txt;h=83e1a027de80d97421564226685a74298d2a5b80;hp=470b765b53eb6c795dc9dfb9ea5c30ec19d25f64;hb=0ab60c7419522ef527d744bc0ad756124b9d432a;hpb=21fe622ab8fe123a3a45369440eaaa3785be2516



Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>