If you try to create empty console app in MSVS 2013 and remove unused references, then only two of them remain: System and System.Core.
But if you preform same task in new MSVS 2015 Community (14.0.23107.0) then nothing except Microsoft.CSharp would be removed:
I think that it is quite strange behavior. All that (actually unused) references used in some temp code file called .NETFramework,Version=v4.6.AssemblyAttributes.cs:
And it is fine if you remove unused references manually - project builds without problems.
The question is: what purpose of that temporary auto-generated file and why it has so many dependencies? It hasn't actually, that is why I suppose that it is bug or something...