Remove an unused field from SuiteSparseCholesky

Change-Id: I63128de3e9806347560ab6f0ebee82ead44f2e45

internal/ceres/suitesparse.h

diff --git a/internal/ceres/suitesparse.h b/internal/ceres/suitesparse.h
index da02cc3..0646602 100644
--- a/internal/ceres/suitesparse.h
+++ b/internal/ceres/suitesparse.h
@@ -296,7 +296,6 @@
   const OrderingType ordering_type_;
   SuiteSparse ss_;
   cholmod_factor* factor_;
-  cholmod_dense* rhs_;
 };
 
 }  // namespace internal