Remove chunk shuffle in multithreaded SchurEliminator

std::random_shuffle() is deprecated since C++14 and was removed in
C++17. At least MSVC with C++17 fails to compile this code, I assume
other compilers fail as well.

In a Github discussion (#373) Sameer Agarwal states this line can
likely be dropped and asks for a PR/CL.

https://github.com/ceres-solver/ceres-solver/issues/373

Change-Id: I78e04f36cba398769b8f90916edbdaf33884e7e1

internal/ceres/schur_eliminator_impl.h

diff --git a/internal/ceres/schur_eliminator_impl.h b/internal/ceres/schur_eliminator_impl.h
index 203dcc9..06d0983 100644
--- a/internal/ceres/schur_eliminator_impl.h
+++ b/internal/ceres/schur_eliminator_impl.h
@@ -151,9 +151,6 @@
   const Chunk& chunk = chunks_.back();
 
   uneliminated_row_begins_ = chunk.start + chunk.size;
-  if (num_threads_ > 1) {
-    random_shuffle(chunks_.begin(), chunks_.end());
-  }
 
   buffer_.reset(new double[buffer_size_ * num_threads_]);