glib: Don't leak GIOChannel when destroying IO handle
glib: Don't leak GIOChannel when destroying IO handle

gvir_event_handle_add() creates a GIOChannel in order to watch the fd it
was given for changes.
gvir_event_handle_remove() is freeing all the resources allocated by
gvir_event_handle_add() except for this GIOChannel. This commit adds
the needed g_io_channel_unref() call to gvir_event_handle_remove()

libvirt/libvirt-glib,libvirt/libvirt-glib,libvirt/libvirt-glib