The enumerations in `vtkm::cont::Field::Association` were renamed in the
previous commit. The old names still exist, but are deprecated. Change
the rest of the code to use the new names.
The `DynamicCellSet` class is now marked as deprecated (as is the header
that contains it), and all non-deprecated code is moved to its
`UnknownCellSet` replacement.
Also added a deprecation warning for the VariantArrayHandle.h header
file and deleted a couple inappropriate uses of it.