The preconditioner `SeqPardiso` using the sparse direct solver
library Pardiso has not been actively maintained for several
years. It is still based on a very old Pardiso version; finding
the library never went into the CMake build system. Moreover,
Pardiso is not open source. With SuperLU and UMFPack, two working
alternative direct solvers are available.

Drop the support for Pardiso by deprecating `SeqPardiso` and
removing the corresponding test.