Refactor: simplify API for configuring cell counts in IJK.

The old API was based on "grid points", but it was always used to
specify number of cells in each direction.

ApplicationLibCode/ProjectDataModel/RimCornerPointCase.cpp

@@ -200,8 +200,8 @@ void RimCornerPointCase::buildGrid( RigEclipseCaseData&       eclipseCaseData,
     RigMainGrid* mainGrid = eclipseCaseData.mainGrid();
     CVF_ASSERT( mainGrid );
 
-    cvf::Vec3st gridPointDim( nx + 1, ny + 1, nz + 1 );
-    mainGrid->setGridPointDimensions( gridPointDim );
+    mainGrid->setCellCounts( cvf::Vec3st( nx, ny, nz ) );
+
     mainGrid->setGridName( "Main grid" );
 
     size_t totalCellCount = nx * ny * nz;