patch 8.1.2024: delete call commented out for debugging

Problem:    Delete call commented out for debugging.
Solution:   Restore the delete call. (Christian Brabandt)
diff --git a/src/testdir/test_undo.vim b/src/testdir/test_undo.vim
index c424273..4a534ae 100644
--- a/src/testdir/test_undo.vim
+++ b/src/testdir/test_undo.vim
@@ -350,7 +350,7 @@
   endfor
 
   bwipe!
-"  call delete('Xundofile')
+  call delete('Xundofile')
 endfunc
 
 " Test for undo working properly when executing commands from a register.