Remove unused filesystem dependency.

Author: Tratcher

src/Microsoft.AspNet.StaticFiles/project.json

@@ -15,8 +15,6 @@
         "System.Diagnostics.Tools": "4.0.0.0",
         "System.Globalization": "4.0.10.0",
         "System.IO": "4.0.0.0",
-        "System.IO.FileSystem": "4.0.0.0",
-        "System.IO.FileSystem.Primitives": "4.0.0.0",
         "System.Linq": "4.0.0.0",
         "System.Reflection": "4.0.10.0",
         "System.Resources.ResourceManager": "4.0.0.0",