Fix compiler warnings. (#7974)

- Remove unused parameters. There are still many warnings that are not yet
addressed. Currently, the warnings in dmlc-core dominate the error log.
- Remove `distributed` parameter from metric.
- Fixes some warnings about signed comparison.

src/learner.cc

@@ -1234,8 +1234,7 @@ class LearnerImpl : public LearnerIO {
 
       obj_->EvalTransform(&out);
       for (auto& ev : metrics_) {
-        os << '\t' << data_names[i] << '-' << ev->Name() << ':'
-           << ev->Eval(out, m->Info(), tparam_.dsplit == DataSplitMode::kRow);
+        os << '\t' << data_names[i] << '-' << ev->Name() << ':' << ev->Eval(out, m->Info());
       }
     }