hxtool: remove dead -q option

This was used to extract .txt documentation for QMP.  This was
changed to use the QAPI schema instead, so zap it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>