Several cleanups.

- Removes dead code.
- Changes to use std::make_unique.

Change-Id: I7921d78606554ca55fbedf719372749663b5464c

internal/ceres/coordinate_descent_minimizer.cc

diff --git a/internal/ceres/coordinate_descent_minimizer.cc b/internal/ceres/coordinate_descent_minimizer.cc
index 298b604..8ecdeff 100644
--- a/internal/ceres/coordinate_descent_minimizer.cc
+++ b/internal/ceres/coordinate_descent_minimizer.cc
@@ -134,8 +134,6 @@
 
   std::vector<std::unique_ptr<LinearSolver>> linear_solvers(
       options.num_threads);
-  // std::unique_ptr<LinearSolver*[]> linear_solvers(
-  //    new LinearSolver*[options.num_threads]);
 
   LinearSolver::Options linear_solver_options;
   linear_solver_options.type = DENSE_QR;
@@ -202,10 +200,6 @@
   for (auto* parameter_block : parameter_blocks_) {
     parameter_block->SetVarying();
   }
-
-  //  for (int i = 0; i < options.num_threads; ++i) {
-  //  delete linear_solvers[i];
-  //}
 }
 
 // Solve the optimization problem for one parameter block.

internal/ceres/covariance_impl.cc

diff --git a/internal/ceres/covariance_impl.cc b/internal/ceres/covariance_impl.cc
index bc4e75f..9957d1d 100644
--- a/internal/ceres/covariance_impl.cc
+++ b/internal/ceres/covariance_impl.cc
@@ -321,9 +321,8 @@
   // Assemble the blocks in the covariance matrix.
   MatrixRef covariance(covariance_matrix, covariance_size, covariance_size);
   const int num_threads = options_.num_threads;
-  std::unique_ptr<double[]> workspace(
-      new double[num_threads * max_covariance_block_size *
-                 max_covariance_block_size]);
+  auto workspace = std::make_unique<double[]>(
+      num_threads * max_covariance_block_size * max_covariance_block_size);
 
   bool success = true;
 
@@ -682,7 +681,7 @@
   // Since the covariance matrix is symmetric, the i^th row and column
   // are equal.
   const int num_threads = options_.num_threads;
-  std::unique_ptr<double[]> workspace(new double[num_threads * num_cols]);
+  auto workspace = std::make_unique<double[]>(num_threads * num_cols);
 
   problem_->context()->EnsureMinimumThreads(num_threads);
   ParallelFor(
@@ -873,7 +872,7 @@
   // are equal.
   const int num_cols = jacobian.num_cols;
   const int num_threads = options_.num_threads;
-  std::unique_ptr<double[]> workspace(new double[num_threads * num_cols]);
+  auto workspace = std::make_unique<double[]>(num_threads * num_cols);
 
   problem_->context()->EnsureMinimumThreads(num_threads);
   ParallelFor(