Specify the number of threads for parallel sort. (#8735)

* Specify the number of threads for parallel sort.

- Pass context object into argsort.
- Replace macros with inline functions.

src/common/common.h

@@ -188,17 +188,6 @@ inline void SetDevice(std::int32_t device) {
 }
 #endif
 
-template <typename Idx, typename Container,
-          typename V = typename Container::value_type,
-          typename Comp = std::less<V>>
-std::vector<Idx> ArgSort(Container const &array, Comp comp = std::less<V>{}) {
-  std::vector<Idx> result(array.size());
-  std::iota(result.begin(), result.end(), 0);
-  auto op = [&array, comp](Idx const &l, Idx const &r) { return comp(array[l], array[r]); };
-  XGBOOST_PARALLEL_STABLE_SORT(result.begin(), result.end(), op);
-  return result;
-}
-
 /**
  * Last index of a group in a CSR style of index pointer.
  */