Clean-up test files.

Also, don't add a Global Settings component at import if the xml doesn't have any global settings (option/size/custom).

PiperOrigin-RevId: 495950899
Change-Id: I6599e8ea3f3a82729fc5c974fd7ced8eb93b277e

unity/Tests/Editor/Tools/MjVFSEditorTests.cs

@@ -55,7 +55,8 @@ namespace Mujoco {
       var filename = "filename";
       var contents = "contents";
       _vfs.AddFile(filename, contents);
-      var filedata = Marshal.PtrToStringAnsi(_vfs.Data.filedata[0]);
+      var fileIndex = _vfs.FindFile(filename);
+      var filedata = Marshal.PtrToStringAnsi(_vfs.Data.filedata[fileIndex]);
       Assert.That(filedata, Is.EqualTo(contents));
     }
   }