Resolve compiler warnings on remote platforms

[spdomin]

Intel-based provides the following warnings:

/projects/netpub/nalu/Nalu/include/LinearSystem.h(85): warning #858: type qualifier on return type is meaningless
const unsigned numDof() const { return numDof_; }
^

/projects/netpub/nalu/Nalu/include/user_functions/WindEnergyTaylorVortexAuxFunction.h(18): warning #654: overloaded virtual function "sierra::nalu::AuxFunction::do_evaluate" is only partially overridden in class "sierra::nalu::WindEnergyTaylorVortexAuxFunction"
class WindEnergyTaylorVortexAuxFunction : public AuxFunction