Remove omp_get_max_threads in tree updaters. (#7590)

include/xgboost/data.h

@@ -302,22 +302,7 @@ class SparsePage {
 
   SparsePage GetTranspose(int num_columns, int32_t n_threads) const;
 
-  void SortRows() {
-    auto ncol = static_cast<bst_omp_uint>(this->Size());
-    dmlc::OMPException exc;
-#pragma omp parallel for schedule(dynamic, 1)
-    for (bst_omp_uint i = 0; i < ncol; ++i) {
-      exc.Run([&]() {
-        if (this->offset.HostVector()[i] < this->offset.HostVector()[i + 1]) {
-          std::sort(
-              this->data.HostVector().begin() + this->offset.HostVector()[i],
-              this->data.HostVector().begin() + this->offset.HostVector()[i + 1],
-              Entry::CmpValue);
-        }
-      });
-    }
-    exc.Rethrow();
-  }
+  void SortRows(int32_t n_threads);
 
   /**
    * \brief Pushes external data batch onto this page

include/xgboost/tree_updater.h

@@ -1,5 +1,5 @@
 /*!
- * Copyright 2014-2019 by Contributors
+ * Copyright 2014-2022 by XGBoost Contributors
  * \file tree_updater.h
  * \brief General primitive for tree learning,
  *   Updating a collection of trees given the information.
@@ -32,7 +32,7 @@ class Json;
  */
 class TreeUpdater : public Configurable {
  protected:
-  GenericParameter const* tparam_;
+  GenericParameter const* ctx_;
 
  public:
   /*! \brief virtual destructor */