Fix some include headers in codegen/test_utils.cc/h

Change-Id: I769029ce2797eba0de6c7baeb76dc3f2782b6305
diff --git a/internal/ceres/codegen/test_utils.cc b/internal/ceres/codegen/test_utils.cc
index c34e773..303c0db 100644
--- a/internal/ceres/codegen/test_utils.cc
+++ b/internal/ceres/codegen/test_utils.cc
@@ -28,7 +28,8 @@
 //
 // Author: darius.rueckert@fau.de (Darius Rueckert)
 
-#include "codegen/test_utils.h"
+#include "ceres/codegen/test_utils.h"
+#include "ceres/test_util.h"
 
 namespace ceres {
 namespace internal {
diff --git a/internal/ceres/codegen/test_utils.h b/internal/ceres/codegen/test_utils.h
index 0a27927..eaaf438 100644
--- a/internal/ceres/codegen/test_utils.h
+++ b/internal/ceres/codegen/test_utils.h
@@ -34,7 +34,6 @@
 #include "ceres/internal/autodiff.h"
 #include "ceres/random.h"
 #include "ceres/sized_cost_function.h"
-#include "test_util.h"
 
 namespace ceres {
 namespace internal {