Disable build for pygtk2 module
    
    The pygtk2 module is orphaned and will be retired from Fedora.
    Also, there is a binding for zbar that claims to support both
    python2 and python3:
    	https://github.com/zplab/zbar-py
    
    Ok, this is currently not packaged on Fedora, but it should be
    easy to install it via pip. So, it may not make much sense to
    change zbar to have a pygtk3 binding.
    
    Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>