namespace to reduce code

src/tree/fit_stump.cu

@@ -21,12 +21,6 @@
 #include "xgboost/logging.h"  // CHECK_EQ
 #include "xgboost/span.h"     // span
 
-#if defined(XGBOOST_USE_HIP)
-namespace thrust {
-    namespace cuda = thrust::hip;
-}
-#endif
-
 namespace xgboost::tree::cuda_impl {
 void FitStump(Context const* ctx, MetaInfo const& info,
               linalg::TensorView<GradientPair const, 2> gpair, linalg::VectorView<float> out) {

src/tree/gpu_hist/evaluate_splits.cu

@@ -24,10 +24,6 @@
 #define WARP_SIZE WAVEFRONT_SIZE
 #endif
 
-#if defined(XGBOOST_USE_HIP)
-namespace cub = hipcub;
-#endif
-
 namespace xgboost::tree {
 // With constraints
 XGBOOST_DEVICE float LossChangeMissing(const GradientPairInt64 &scan,

src/tree/gpu_hist/evaluator.cu

@@ -12,12 +12,6 @@
 #include "evaluate_splits.cuh"
 #include "xgboost/data.h"
 
-#if defined(XGBOOST_USE_HIP)
-namespace thrust {
-    namespace cuda = thrust::hip;
-}
-#endif
-
 namespace xgboost::tree {
 void GPUHistEvaluator::Reset(common::HistogramCuts const &cuts, common::Span<FeatureType const> ft,
                              bst_feature_t n_features, TrainParam const &param,

src/tree/gpu_hist/histogram.cu

@@ -16,12 +16,6 @@
 #include "row_partitioner.cuh"
 #include "xgboost/base.h"
 
-#if defined(XGBOOST_USE_HIP)
-namespace thrust {
-    namespace cuda = thrust::hip;
-}
-#endif
-
 namespace xgboost {
 namespace tree {
 namespace {