Update signs_description.xml

[digitalheir]

Fixes first half of #37:

• Aa18 is a denoted to contain Aa17, but also vice versa. I think it is clear that Aa17 does not include Aa18.
• V98 is a denoted to contain V36, but also vice versa. I think it is clear that V98 does not include V36.
• Y1 is a denoted to contain Y2, but also vice versa. I think it is clear that Y2 does not include Y1.
• D32 is a denoted to contain D197, but also vice versa. I think it is clear that D197 does not include D32.