STYLE: avoid old-style shell backticks in various places

bin/foamEtcFile

bin/foamPack

bin/foamRunTutorials

etc/bashrc

etc/config.csh/ensight

etc/config.csh/settings

etc/config.sh/ensight

etc/config.sh/functions

etc/config.sh/mpi

etc/config.sh/settings

etc/config.sh/unset

etc/cshrc

etc/templates/axisymmetricJet/Allrun

.../compressible/rhoCentralFoam/biconic25-55Run35/sampleCone

...r/buoyantSimpleFoam/buoyantCavity/validation/createGraphs

...egionFoam/externalCoupledMultiRegionHeater/externalSolver

...ressible/boundaryFoam/boundaryWallFunctionsProfile/Allrun

...rangian/reactingParcelFilmFoam/hotBoxes/patchifyObstacles

tutorials/multiphase/interFoam/RAS/waterChannel/Allmesh