A little script to get a clean name after a duplication or a copy of a gameobject in your unity scene. Drag and drop it into an editor folder !

CleanDuplicateName.cs

using System.Text.RegularExpressions;
using UnityEditor;
using UnityEngine;

[InitializeOnLoad]
public class CleanDuplicateName
{
    static bool eventDuplicateAppend;

    static CleanDuplicateName()
    {
        EditorApplication.hierarchyWindowItemOnGUI += (int instanceID, Rect selectionRect) =>
        {
            if(Event.current != null && Event.current.type == EventType.ExecuteCommand && (Event.current.commandName == "Duplicate" || Event.current.commandName == "Paste"))
                eventDuplicateAppend = true;
        };

        EditorApplication.hierarchyChanged += () =>
        {
            if(eventDuplicateAppend)
            {
                foreach (GameObject iGamebject in Selection.gameObjects)
                    iGamebject.name = Regex.Replace(iGamebject.name, @"(.*)\s\([0-9]*\)", @"$1");
            }
            eventDuplicateAppend = false;
        };
    }
}