Don't Provide Deck Accessors in FlowMainEbos

Following commits f4f8c033d and c7016854d (PR #4286), the "vanguard"
no longer maintains an internal Deck data member.  Don't pretend
that it does by providing member functions to access that data
member.  If someone tries to actually call these member functions
then they will get an unfriendly diagnostic message and a build
failure.

opm/simulators/flow/FlowMainEbos.hpp

@@ -431,12 +431,6 @@ void handleExtraConvergenceOutput(SimulatorReport& report,
             }
         }
 
-        const Deck& deck() const
-        { return ebosSimulator_->vanguard().deck(); }
-
-        Deck& deck()
-        { return ebosSimulator_->vanguard().deck(); }
-
         const EclipseState& eclState() const
         { return ebosSimulator_->vanguard().eclState(); }