Properly detect System.Private library

[ForNeVeR]

In scope of #195, we have this line.

I think that it looks like a hack. @impworks have explained to me that System.Private DLL is duplicating the main framework types, so LENS get confused about them.

Probably that's a type-forwarded assembly and we need to add type forwarding support to LENS or something like that. Requires additional research (I hope that it's a simple task).