petsc: add setupHook to set PETSC_DIR env

pkgs/by-name/pe/petsc/package.nix

···
     inherit mpiSupport;
   };
 
+  setupHook = ./setup-hook.sh;
+
   meta = with lib; {
     description = "Portable Extensible Toolkit for Scientific computation";
     homepage = "https://petsc.org/release/";

pkgs/by-name/pe/petsc/setup-hook.sh

···
+export PETSC_DIR=@out@

pkgs/by-name/pf/pflotran/package.nix

···
       --subst-var-by "HDF5_FORTRAN_INCLUDE" "${lib.getDev hdf5-fortran-mpi}/include"
   '';
 
-  configureFlags = [
-    "--with-petsc-dir=${petsc}"
-    "--with-petsc-arch=linux-gnu-c-release"
-  ];
-
   meta = with lib; {
     description = "Parallel, multi-physics simulation code for subsurface flow and transport";
     homepage = "https://pflotran.org/";