Remove redundant test setup, which isn't XFS compat

Author: tathamoddie

TestHelpers.Tests/MockDirectoryTests.cs

@@ -383,11 +383,7 @@ public void MockDirectory_Exists_ShouldReturnTrueForFolderContainingFileAddedToM
         public void MockDirectory_Exists_ShouldReturnFalseForIllegalPath(string path)
         {
             // Arrange
-            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
-            {
-                { @"c:\foo\bar.txt", new MockFileData("Demo text content") },
-                { @"c:\baz.txt", new MockFileData("Demo text content") }
-            });
+            var fileSystem = new MockFileSystem();
 
             // Act
             var result = fileSystem.Directory.Exists(path);