Deprecate SQLite Extensions MvvmCross package

[Iain Smith]

The MvvmCross team have removed the MvvmCross.Community.Plugin.Sqlite package.

You can read more here so I think we should deprecate the SQLiteNetExtensions-MvvmCross package and remove the code. If anyone still needs it they can use the versions 2.0.0 and lower.