ObjectValue::set_visited(bool) sets _visited false

The setter is error-prone. it unconditionally sets _visited false.
it's useless because the member variable is initialized to false.

file: debuginfo.hpp
class ObjectValue: public ScopeValue {
...
  void set_visited(bool visited) { _visited = false; }
}

link: https://github.com/openjdk/jdk/blob/master/src/hotspot/share/code/debugInfo.hpp#L152