Make Manor deletable

Well, this thread is about the British manor so I don’t discuss too many other buildings.

Forts can be built by European explorers after sending the card. If you want to discuss about factories or wonders, you can create another thread. In fact, there is already a similar thread.

However, those important buildings can still be deleted by the player even if they cannot be rebuilt.
As a building, it is very counter-intuitive to design that the manor cannot be deleted.