mostly eliminate Eigen in the FIP and VFP code

this code mostly used the Eigen vectors as arrays anyway, so let's use
`std::vector`.

also, this patch only "mostly eliminates" Eigen from from these parts
of the code because the source files of the VFP code still use
AutoDiffBlock; Unfortunately this cannot easily be changed because
`flow_legacy` depends on these methods. (`flow_ebos` does not use the
incriminating methods.)

opm/autodiff/BlackoilModelBase.hpp

@@ -268,7 +268,7 @@ namespace Opm {
         /// \param[in]    ReservoirState
         /// \param[in]    FIPNUM for active cells not global cells.
         /// \return fluid in place, number of fip regions, each region contains 5 values which are liquid, vapour, water, free gas and dissolved gas.
-        std::vector<V>
+        std::vector<std::vector<double> >
         computeFluidInPlace(const ReservoirState& x,
                             const std::vector<int>& fipnum);