ClangTidy cleanups

1. NULL -> nullptr
2. foo.reset(new Bar) -> = foo = std::make_unique<Bar>()
3. Missing std library includes & prefixes

Change-Id: I260b261b484554be681ee5a7398126fdb3b3a789
diff --git a/internal/ceres/generate_bundle_adjustment_tests.py b/internal/ceres/generate_bundle_adjustment_tests.py
index 7b0caa3..86b4fcb 100644
--- a/internal/ceres/generate_bundle_adjustment_tests.py
+++ b/internal/ceres/generate_bundle_adjustment_tests.py
@@ -137,7 +137,7 @@
   options->sparse_linear_algebra_library_type = %(sparse_backend)s;
   options->preconditioner_type = %(preconditioner)s;
   if (%(ordering)s) {
-    options->linear_solver_ordering.reset();
+    options->linear_solver_ordering = nullptr;
   }
   Problem* problem = bundle_adjustment_problem.mutable_problem();
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);