Fix two unused variable warnings.

Change-Id: Iaabb47ea45aa09d92b911df79b4f2fd7ee60ae15

internal/ceres/manifold.cc

diff --git a/internal/ceres/manifold.cc b/internal/ceres/manifold.cc
index 8163d2c..365d5d6 100644
--- a/internal/ceres/manifold.cc
+++ b/internal/ceres/manifold.cc
@@ -299,7 +299,6 @@
 bool SubsetManifold::MinusJacobian(const double* x,
                                    double* minus_jacobian) const {
   const int ambient_size = AmbientSize();
-  const int tangent_size = TangentSize();
   MatrixRef m(minus_jacobian, tangent_size_, ambient_size);
   m.setZero();
   for (int c = 0, r = 0; c < ambient_size; ++c) {

internal/ceres/manifold_test.cc

diff --git a/internal/ceres/manifold_test.cc b/internal/ceres/manifold_test.cc
index f626430..73a6138 100644
--- a/internal/ceres/manifold_test.cc
+++ b/internal/ceres/manifold_test.cc
@@ -85,7 +85,6 @@
 
 // Checks that the invariant Minus(x, x) == 0 holds.
 MATCHER_P(XMinusXIsZeroAt, x, "") {
-  const int ambient_size = arg.AmbientSize();
   const int tangent_size = arg.TangentSize();
   Vector actual = Vector::Zero(tangent_size);
   EXPECT_TRUE(arg.Minus(x.data(), x.data(), actual.data()));