tutorials: Removed 0.orig directories in favor of <field>.orig

The new automated <field>.orig reading has made 0.orig directories and
associated scripting redundant.

bin/tools/CleanFunctions

@@ -78,7 +78,7 @@ cleanCase()
     rm -rf VTK > /dev/null 2>&1
     rm -rf sequencedVTK > /dev/null 2>&1
 
-    rm -f 0/cellLevel 0/pointLevel 0/cellDist constant/cellDecomposition
+    rm -f 0/polyMesh 0/cellLevel 0/pointLevel 0/cellDist constant/cellDecomposition
 
     if [ -e system/blockMeshDict.m4 ]
     then