Fix projects definitions

AdventOfCode2020/Day04.cs

@@ -1,7 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-
+namespace AdventOfCode2020;
 
 /*
 --- Day 4: Passport Processing ---
@@ -124,8 +121,6 @@ Count the number of valid passports - those that have all required fields and va
  
 */
 
-namespace AdventOfCode2020;
-
 public class Day04 : IDay
 {
     public string ResolvePart1(string[] inputs)