vim-patch:partial:9.0.0719: too many delete() calls in tests

Problem:    Too many delete() calls in tests.
Solution:   Use deferred delete where possible.

56564964e6

This includes all changes expect changes in test_startup.vim.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

test/old/testdir/test_sort.vim

@@ -1525,11 +1525,10 @@ func Test_sort_with_no_last_search_pat()
     call writefile(v:errors, 'Xresult')
     qall!
   [SCRIPT]
-  call writefile(lines, 'Xscript')
+  call writefile(lines, 'Xscript', 'D')
   if RunVim([], [], '--clean -S Xscript')
     call assert_equal([], readfile('Xresult'))
   endif
-  call delete('Xscript')
   call delete('Xresult')
 endfunc