Ramsey: use information from transformed model for filling M_.nonzero_hessian_eqs

Since commit 9c9e8f81, it’s the information
from the original model which was in this field, which is not what is expected.

By the way, do not output this field (and the related M_.hessian_eq_zero) when
the Hessian is not computed by the preprocessor (i.e. in practice for perfect
foresight), since they would otherwise contain incorrect information.

Ref. dynare#1681