Resolve unnecessary import of thrust/optional.hpp in types.hpp (#7667)

Resolves #6475. The missing required include of `optional.hpp` was in `convert_datetime.cu`.

Authors:
  - Vyas Ramasubramani (@vyasr)

Approvers:
  - Conor Hoekstra (@codereport)
  - Jake Hemstad (@jrhemstad)
  - Mark Harris (@harrism)

URL: #7667

cpp/include/cudf/io/parquet.hpp

@@ -24,6 +24,8 @@
 
 #include <rmm/mr/device/per_device_resource.hpp>
 
+#include <thrust/optional.h>
+
 #include <iostream>
 #include <memory>
 #include <string>

cpp/include/cudf/types.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,8 +24,6 @@
 #define CUDA_DEVICE_CALLABLE inline
 #endif
 
-#include <thrust/optional.h>  // TODO no idea why this is needed ¯\_(ツ)_/¯
-
 #include <cassert>
 #include <cstddef>
 #include <cstdint>

cpp/src/lists/explode.cu

@@ -29,6 +29,7 @@
 #include <thrust/binary_search.h>
 #include <thrust/iterator/counting_iterator.h>
 #include <thrust/iterator/transform_iterator.h>
+#include <thrust/optional.h>
 
 #include <memory>
 #include <type_traits>

cpp/src/strings/convert/convert_datetime.cu

@@ -35,6 +35,7 @@
 #include <rmm/device_uvector.hpp>
 
 #include <thrust/logical.h>
+#include <thrust/optional.h>
 
 #include <map>
 #include <vector>