Fix projects definitions

AdventOfCode2020/Day06.cs

@@ -1,6 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
+namespace AdventOfCode2020;
 
 /*
 
@@ -52,8 +50,6 @@ For each group, count the number of questions to which anyone answered "yes". Wh
 
 */
 
-namespace AdventOfCode2020;
-
 public class Day06 : IDay
 {
     public string ResolvePart1(string[] inputs)