Revert the EditorBuildSetting file

Project/ProjectSettings/EditorBuildSettings.asset

 EditorBuildSettings:
   m_ObjectHideFlags: 0
   serializedVersion: 2
-  m_Scenes:
-  - enabled: 1
-    path: Assets/ML-Agents/Examples/3DBall/Scenes/3DBallHard.unity
-    guid: 35c41099ceec44889bdbe95ed86c97ac
+  m_Scenes: []
   m_configObjects: {}