Fix subnet creation tip that mentions TAO is returned when the subnet is deregistered

[titan-hashwalker]

In this section of the docs:

https://github.com/opentensor/developer-docs/blob/main/docs/subnets/create-a-subnet.md

In both Test Chain and Main Chain sections:

It is mentioned that the TAO is returned when a subnet is deregistered. However, a subnet cannot be deregistered in the first place (post dTAO), and second, the TAO is burned entirely and not returned.