gtk4 parse_options(): Check against unknown options
As comment in gtk4 parse_options() notes:
gtk commandline options have already been dropped from the gtk4 development version gtk3x-client currently uses.
Also, the same TODO comment in gtk3.22-client makes no sense - gtk+-3 API is not going to change. Removing that comment applies even to S3_0.
As comment in gtk4 parse_options() notes:
gtk commandline options have already been dropped from the gtk4 development version gtk3x-client currently uses.