Bound the size of the histogram cache. (#9440)

- A new histogram collection with a limit in size.
- Unify histogram building logic between hist, multi-hist, and approx.

src/common/hist_util.cc

@@ -67,17 +67,6 @@ HistogramCuts SketchOnDMatrix(Context const *ctx, DMatrix *m, bst_bin_t max_bins
   return out;
 }
 
-/*!
- * \brief fill a histogram by zeros in range [begin, end)
- */
-void InitilizeHistByZeroes(GHistRow hist, size_t begin, size_t end) {
-#if defined(XGBOOST_STRICT_R_MODE) && XGBOOST_STRICT_R_MODE == 1
-  std::fill(hist.begin() + begin, hist.begin() + end, xgboost::GradientPairPrecise());
-#else  // defined(XGBOOST_STRICT_R_MODE) && XGBOOST_STRICT_R_MODE == 1
-  memset(hist.data() + begin, '\0', (end - begin) * sizeof(xgboost::GradientPairPrecise));
-#endif  // defined(XGBOOST_STRICT_R_MODE) && XGBOOST_STRICT_R_MODE == 1
-}
-
 /*!
  * \brief Increment hist as dst += add in range [begin, end)
  */