ui/vc: do not parse VC-specific options in Spice and GTK

ui/vc: do not parse VC-specific options in Spice and GTK

In commit 6f974c843c ("gtk: overwrite the console.c char driver"), I
shared the VC console parse handler with GTK. And later on in commit
d8aec9d9 ("display: add -display spice-app launching a Spice client"),
I also used it to handle spice-app VC.

This is not necessary, the VC console options (width/height/cols/rows)
are specific, and unused by tty-level GTK/Spice VC.

This is not a breaking change, as those options are still being parsed
by QAPI ChardevVC. Adjust the documentation about it.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230830093843.3531473-44-marcandre.lureau@redhat.com>