No device needs them anymore and in fact they're undocumented.
Remove the code.  The only change in behavior is that "-usbdevice
braille:hello" now reports an error, which is a bugfix.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210310173323.1422754-2-thuth@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>