patch 8.2.4467: running filetype test leaves file behind

Problem:    Running filetype test leaves file behind.
Solution:   Delete the file.
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index 56288d7..0b65119 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -862,6 +862,7 @@
   call assert_equal('d', &filetype)
   bwipe!
 
+  " clean up
   filetype off
   call delete('Xfile.d')
 endfunc