patch 8.1.0208: file left behind after running individual test

Problem:    File left behind after running individual test.
Solution:   Delete the file.
diff --git a/src/testdir/test_modeline.vim b/src/testdir/test_modeline.vim
index e278c16..f02c68c 100644
--- a/src/testdir/test_modeline.vim
+++ b/src/testdir/test_modeline.vim
@@ -5,4 +5,5 @@
   call writefile(['vi:0', 'nothing'], 'Xmodeline')
   call assert_fails('split Xmodeline', 'E518:')
   bwipe!
+  call delete('Xmodeline')
 endfunc