Fix compiler warnings. (#8022)

- Remove/fix unused parameters
- Remove deprecated code in rabit.
- Update dmlc-core.

src/gbm/gblinear.cc

@@ -148,8 +148,8 @@ class GBLinear : public GradientBooster {
     monitor_.Stop("DoBoost");
   }
 
-  void PredictBatch(DMatrix *p_fmat, PredictionCacheEntry *predts,
-                    bool training, unsigned layer_begin, unsigned layer_end) override {
+  void PredictBatch(DMatrix* p_fmat, PredictionCacheEntry* predts, bool /*training*/,
+                    uint32_t layer_begin, uint32_t) override {
     monitor_.Start("PredictBatch");
     LinearCheckLayer(layer_begin);
     auto* out_preds = &predts->predictions;
@@ -157,9 +157,8 @@ class GBLinear : public GradientBooster {
     monitor_.Stop("PredictBatch");
   }
   // add base margin
-  void PredictInstance(const SparsePage::Inst &inst,
-                       std::vector<bst_float> *out_preds,
-                       unsigned layer_begin, unsigned layer_end) override {
+  void PredictInstance(const SparsePage::Inst& inst, std::vector<bst_float>* out_preds,
+                       uint32_t layer_begin, uint32_t) override {
     LinearCheckLayer(layer_begin);
     const int ngroup = model_.learner_model_param->num_output_group;
     for (int gid = 0; gid < ngroup; ++gid) {
@@ -172,9 +171,9 @@ class GBLinear : public GradientBooster {
     LOG(FATAL) << "gblinear does not support prediction of leaf index";
   }
 
-  void PredictContribution(DMatrix* p_fmat,
-                           HostDeviceVector<bst_float>* out_contribs,
-                           unsigned layer_begin, unsigned layer_end, bool, int, unsigned) override {
+  void PredictContribution(DMatrix* p_fmat, HostDeviceVector<bst_float>* out_contribs,
+                           uint32_t layer_begin, uint32_t /*layer_end*/, bool, int,
+                           unsigned) override {
     model_.LazyInitModel();
     LinearCheckLayer(layer_begin);
     auto base_margin = p_fmat->Info().base_margin_.View(GenericParameter::kCpuId);
@@ -210,9 +209,9 @@ class GBLinear : public GradientBooster {
     }
   }
 
-  void PredictInteractionContributions(DMatrix* p_fmat,
-                                       HostDeviceVector<bst_float>* out_contribs,
-                                       unsigned layer_begin, unsigned layer_end, bool) override {
+  void PredictInteractionContributions(DMatrix* p_fmat, HostDeviceVector<bst_float>* out_contribs,
+                                       unsigned layer_begin, unsigned /*layer_end*/,
+                                       bool) override {
     LinearCheckLayer(layer_begin);
     std::vector<bst_float>& contribs = out_contribs->HostVector();
 

src/gbm/gblinear_model.h

@@ -34,7 +34,10 @@ struct DeprecatedGBLinearModelParam : public dmlc::Parameter<DeprecatedGBLinearM
     std::memset(this, 0, sizeof(DeprecatedGBLinearModelParam));
   }
 
-  DMLC_DECLARE_PARAMETER(DeprecatedGBLinearModelParam) {}
+  DMLC_DECLARE_PARAMETER(DeprecatedGBLinearModelParam) {
+    DMLC_DECLARE_FIELD(deprecated_num_feature);
+    DMLC_DECLARE_FIELD(deprecated_num_output_group);
+  }
 };
 
 // model for linear booster

src/gbm/gbtree.h

@@ -236,10 +236,6 @@ class GBTree : public GradientBooster {
   void SaveModel(Json* p_out) const override;
   void LoadModel(Json const& in) override;
 
-  bool AllowLazyCheckPoint() const override {
-    return model_.learner_model_param->num_output_group == 1;
-  }
-
   // Number of trees per layer.
   auto LayerTrees() const {
     auto n_trees = model_.learner_model_param->num_output_group * model_.param.num_parallel_tree;