Removed Nubia

With one nation already satisfying the Nubia formation requirements
(>80% of Nubian provinces), the decision is made to drop Nubia as a
formable nation.
Updated formable nations for 1.8

Formable nations have been updated to use the new provinces added in
1.8. Also the custom regions have been removed and those decisions which
used them now use the counting condition added in 1.8. Resolves #49