Fix: make EXX symmetry consistent with the fixed irreducible k-points

[maki49]

To rotate the density matrices correctly, module_exx_symmetry must be consistent with kv.kstars set in ibz_kpoint.
However, during cell-relax, k-points are not reduced again when the symmetry changes. Such inconsistency make it impossible to rotate the density matrices using the changed symmetry.

As a temporary solution, I move the initialization of EXX symmetry into before_all_runners. It will be called only once after ibz_kpoints.

If the irreducible k-points can change with symmetry during cell-relax, it can be moved back to before_scf.