[freeflow] Remove property NormalizePressure
When enabled, all pressure related calculations for the momentum equations are done with
p - p_const. The idea was to lower the numerical values of the pressure in the hope of decreasing numerical errors when further processing the values in for the Jacobian. However,
p - p_const probably already introduces the same error we wanted to avoid in the first place.
The property and the pressure normalization should therefore be removed after a check of the Matrix' condition number.