Disable building of cups driver in host-gutenprint

This should fix http://autobuild.buildroot.org/results/d2e386b50744aeda7257a0b78aafe90ba4da697c/


Because there is no host-cups package, host-gutenprint cant build the
host-cups drivers - missing includes and libs.  Host gutenprint only
built to get the xml. Thus not a loss.

Signed-off-by: Olivier Schonken <olivier.schonken@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>