Removed unused XML references on Android Project.
Removed unused XML references on iOS Project.
Removed unused XML references on Ouya Project.
Removed unused XML references on Linux Project.
Removed unused XML references on MacOS Project.
Removed unused XML references on WindowsGL Project.
Removed unused XML references on Windows Project.
Also removed System.Xml references on Lidgren.
Added back Lidgren references to System.Xml, since it needs it.
Added back WindowsGL references to System.Xml and System.Xml.Linq.
Removed unnecessary using on GamePad class.
Merge pull request #1994 from azchohfi/androidRemoveUnusedReferences

Removed unused XML references on MonoGame Project's.