[cleanup][tests] Use new standard grid creator for stokes2cni

* Use input file for structured grids instead of dgf files for
  stokes2cni tests

test/freeflow/stokes2cni/grids/test_stokes2cni.dgf

-DGF
-Interval
-0 0   % first corner 
-1.0 1.0 % second corner
-18 18 % 120 30   % 24 cells in x and 16 in y direction
-# 
-#GridParameter
-#overlap 0 
-#periodic 
-#closure green
-#copies none
-#heapsize 500
-BOUNDARYDOMAIN
-default 1    % all boundaries have id 1
-#BOUNDARYDOMAIN
-# unitcube.dgf 

test/freeflow/stokes2cni/stokes2cnitestproblem.hh

@@ -23,8 +23,6 @@
 #ifndef DUMUX_STOKES2CNITESTPROBLEM_HH
 #define DUMUX_STOKES2CNITESTPROBLEM_HH
 
-#include <dune/grid/io/file/dgfparser/dgfyasp.hh>
-
 #if HAVE_PARDISO
 #include <dumux/linear/pardisobackend.hh>
 #endif

test/freeflow/stokes2cni/test_stokes2cni.input

@@ -3,7 +3,9 @@ DtInitial = 0.1 # [s]
 TEnd = 3 # [s]
 
 [Grid]
-File = ./grids/test_stokes2cni.dgf
+LowerLeft = 0 0
+UpperRight = 1 1
+Cells = 18 18
 
 [Stokes]
 StabilizationAlpha = -1.0 # a stabilization factor. Set to zero for no stabilization

test/freeflow/stokes2cni/test_stokes2cni_conduction.input

@@ -3,7 +3,9 @@ DtInitial = 0.1 # [s]
 TEnd = 3 # [s]
 
 [Grid]
-File = ./grids/test_stokes2cni.dgf
+LowerLeft = 0 0
+UpperRight = 1 1
+Cells = 18 18
 
 [Stokes]
 StabilizationAlpha = -1.0 # a stabilization factor. Set to zero for no stabilization