rename the 'flow' binary to 'flow_legacy' and set a symbolic link

this is a precursor of merging flow_ebos into the master
branch. hopefully, this won't break any existing setups...

examples/flow.cpp

@@ -1,42 +0,0 @@
-/*
-  Copyright 2013, 2014, 2015 SINTEF ICT, Applied Mathematics.
-  Copyright 2014 Dr. Blatt - HPC-Simulation-Software & Services
-  Copyright 2015 IRIS AS
-
-  This file is part of the Open Porous Media project (OPM).
-
-  OPM is free software: you can redistribute it and/or modify
-  it under the terms of the GNU General Public License as published by
-  the Free Software Foundation, either version 3 of the License, or
-  (at your option) any later version.
-
-  OPM is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public License
-  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
-*/
-
-
-#if HAVE_CONFIG_H
-#include "config.h"
-#endif // HAVE_CONFIG_H
-
-
-#include <opm/core/grid.h>
-#include <opm/autodiff/SimulatorFullyImplicitBlackoil.hpp>
-#include <opm/autodiff/FlowMain.hpp>
-
-
-// ----------------- Main program -----------------
-int
-main(int argc, char** argv)
-{
-    typedef UnstructuredGrid Grid;
-    typedef Opm::SimulatorFullyImplicitBlackoil<Grid> Simulator;
-
-    Opm::FlowMain<Grid, Simulator> mainfunc;
-    return mainfunc.execute(argc, argv);
-}