Update using directives in generator templates (#2416)

Author: ErikSchierboom

exercises/practice/accumulate/.meta/Generator.tpl

@@ -14,8 +14,6 @@ end }}
             ret "int[]"
     end
 end }}
-using System.Linq;
-using Xunit;
 
 public class {{ testClass }}
 {

exercises/practice/acronym/.meta/Generator.tpl

@@ -1,5 +1,3 @@
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}

exercises/practice/affine-cipher/.meta/Generator.tpl

@@ -1,6 +1,3 @@
-using System;
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}

exercises/practice/all-your-base/.meta/Generator.tpl

@@ -1,6 +1,3 @@
-using System;
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}

exercises/practice/allergies/.meta/Generator.tpl

@@ -1,5 +1,3 @@
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests | property "allergicTo" }}

exercises/practice/alphametics/.meta/Generator.tpl

@@ -1,7 +1,3 @@
-using System;
-using System.Collections.Generic;
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}

exercises/practice/anagram/.meta/Generator.tpl

@@ -1,5 +1,3 @@
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}

exercises/practice/armstrong-numbers/.meta/Generator.tpl

@@ -1,5 +1,3 @@
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}

exercises/practice/atbash-cipher/.meta/Generator.tpl

@@ -1,5 +1,3 @@
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}

exercises/practice/bank-account/.meta/Generator.tpl

@@ -18,12 +18,6 @@ end }}
     ret $"{to_tested_method $0}({ to_amount $0 })"
 end }}
 
-
-using System;
-using System.Collections.Generic;
-using System.Threading.Tasks;
-using Xunit;
-
 public class {{ testClass }}
 {
     {{- for test in tests }}