patch 9.0.0625: too many delete() calls in tests

Problem:    Too many delete() calls in tests.
Solution:   Use deferred delete where possible.
diff --git a/src/testdir/test_listchars.vim b/src/testdir/test_listchars.vim
index 0977543..b9b078c 100644
--- a/src/testdir/test_listchars.vim
+++ b/src/testdir/test_listchars.vim
@@ -664,7 +664,7 @@
       vsplit
       windo set signcolumn=yes foldcolumn=1 winminwidth=0 nowrap list listchars=extends:>,precedes:<
   END
-  call writefile(lines, 'XTest_listchars')
+  call writefile(lines, 'XTest_listchars', 'D')
 
   let buf = RunVimInTerminal('-S XTest_listchars', {'rows': 10, 'cols': 60})
 
@@ -687,7 +687,6 @@
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('XTest_listchars')
 endfunc