rhoMax/rhoMin defined but not used in buoyantSimpleFoam
In the solver applications/solvers/heatTransfer/buoyantSimpleFoam, the rhoMax and rhoMin variables are defined in createFields.H, but never used in this solver.
I noticed this today with v1806, but have checked and this also occurs in v1812 and v1906-rc1.
According to git blame, the commit 1a701d9eac55a49f22b983683826d3ead8a8c85b is when this was added, but the min-max restriction was not imposed into this solver, the same way it was in chtMultiRegionSimpleFoam: https://develop.openfoam.com/Development/OpenFOAM-plus/blob/1a701d9eac55a49f22b983683826d3ead8a8c85b/applications/solvers/heatTransfer/chtMultiRegionFoam/chtMultiRegionSimpleFoam/fluid/pEqn.H#L91
## Reattaching the author to the issue ticket: @wyldckat ##
