patch 9.0.0538: manually deleting test temp files

Problem:    Manually deleting test temp files.
Solution:   Add the 'D' flag to writefile().
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index 8e2345d..b478963 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -706,13 +706,12 @@
     call writefile([execute('messages')], 'Xtest.out')
     qall
   END
-  call writefile(cleanup, 'Xverify.vim')
+  call writefile(cleanup, 'Xverify.vim', 'D')
   call RunVim([], [], "-c \"echo function('s:abc')\" -S Xverify.vim")
   call assert_match('E81: Using <SID> not in a', readfile('Xtest.out')[0])
   call RunVim([], [], "-c \"echo funcref('s:abc')\" -S Xverify.vim")
   call assert_match('E81: Using <SID> not in a', readfile('Xtest.out')[0])
   call delete('Xtest.out')
-  call delete('Xverify.vim')
 endfunc
 
 func Test_setmatches()