STYLE: avoid old-style shell backticks in various places

tutorials/multiphase/interFoam/RAS/waterChannel/Allmesh

@@ -4,17 +4,14 @@ cd ${0%/*} || exit 1    # Run from this directory
 # Source tutorial run functions
 . $WM_PROJECT_DIR/bin/tools/RunFunctions
 
-application=$(getApplication)
-
 runApplication blockMesh
 
 echo "Creating channel"
-i=1
-while [ "$i" -lt 3 ] ; do
+for i in 1 2
+do
     cp system/extrudeMeshDict.${i} system/extrudeMeshDict
     echo "Running extrudeMesh, instance" ${i}
     extrudeMesh > log.extrudeMesh.${i}
-    i=`expr $i + 1`
 done
 
 #------------------------------------------------------------------------------