Unused usings should be removed

[jterry75]

If a file contains a using declaration that is not actually used it should be removed.

using System;
using System.Collections.Generic;

class Test
{
    public static void Main()
    {
        Console.WritLine("not using generics");
    }
}

[amanda-mitchell]

I would like to take this one.

From my understanding, support for this would require a new ILocalSemanticFormattingRule that would run the diagnostics looking for CS8019 warnings and removing the offending using directives. As in the UsingLocationRule, files with preprocessor directives should probably be ignored.

[Daniel-Svensson]

It would be great if you could specify some namespaces which should always be kept such as System.Linq.