Unable to remove old dll dependencies


I have noticed that apk archive that I am exporting using Unity3D contains dlls that I am not using in my project any more.
System.dll (used for Queue)
System.Core.dll (used for extensions)

I am not using Queues and extensions any more.

I have looked into Assembly-CSharp.dll with ildasm.exe from Microsoft SDK and there is only usage of mscorlib.dll. Nothing more. And I accept that.

But why Unity still remembers previously used dlls? Is there any cache that I need to clear?

I am using Unity3D 4.6.2p1


And again, I am answering my own question.

It turned out that System.dll and System.Core.dll are used by UnityEngine.UI

System.dll for ObjectPool:


System.Core.dll for LayoutUtility and ToggleGroup:


Please anyone, confirm that is an unnoticed bug in Engine?