Silence unused arguments warnings
    
    In file included from virt-viewer-session-spice.c:41:
    gbinding.c: In function 'on_source_notify':
    gbinding.c:381: warning: unused parameter 'gobject'
    gbinding.c: In function 'on_target_notify':
    gbinding.c:422: warning: unused parameter 'gobject'
    gbinding.c: In function 'g_binding_init':
    gbinding.c:709: warning: unused parameter 'binding'